■I 


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6 

PRINCETON,    N.    J. 

Section    ..     0>?„./p 
Number. ...Vl.  ft .. 

THE  EVOLUTION  OF  MAN, 


Digitized  by  the  Internet  Archive 

in  2011  with  funding  from 

Princeton  Theological  Seminary  Library 


http://www.archive.org/details/evolutionofm02haec 


THE 

EVOLUTION    OF    MAN 

A  POPULAR  EXPOSITION 


PRINCIPAL  POIXTS  OF  HUMAN  ONTOGENY  AND  PHYLOGENY. 


FROM   THE    GERMAN   OF 

ERNST    HAECKEL, 

PROFESSOR  IN  THE    UNIVERSITY   OP  JENA, 
AUTHOR     OP    "THE    HISTORY    OF    CREATION,"    ETC. 


IN    TWO    VOLUMES. 
VOL.  II. 


NEW  YORK : 
D.  APPLETON  AND  COMPANY, 

549    &    551    BROADWAY. 

1879. 


CONTENTS   OF   VOL.   II. 


PACE 

List  of  Plates        xUi 

List  of  Woodcuts  ...  ...  ...  •••  •••  x1^ 

List  of  Genetic  Tables         ...  ...  ...  •••  —    xvu 


CHAPTER  XV. 

THE  DURATION  OF  HUMAN  TRIBAL  HISTORY. 

Comparison  of  Ontogenetic  and  Phylogenetic  Periods  of  Time. — Dura- 
tion of  Germ-history  in  Man  and  in  Different  Animals. — Extreme 
Brevity  of  the  Latter  in  Comparison  with  the  Immeasurable  Long 
Periodii  of  Tribal  History. — Relation  of  this  Rapid  Ontogenetic 
Modification  to  the  Slow  Phylogenetic  Metamorphosis. — Estimate 
of  the  Past  Duration  of  the  Organic  World,  founded  on  the  Relative 
Thickness  of  Sedimentary  Rock-strata,  or  Neptunian  Formations. 
— The  Five  Main  Divisions  in  the  Latter :  I.  Primordial,  or 
Archilithic  Epoch.  II.  Primary,  or  Palajolithic  Epoch.  III.  Second- 
ary, or  Mesolithic  Epoch.  IV.  Tertiary,  or  Casnolithic  Epoch. 
V.  Quaternary,  or  Anthropolithic  Epoch. — The  Relative  Duration 
of  the  Five  Epochs. — The  Results  of  Comparative  Philology  as 
Explaining  the  Phylogeny  of  Species. — The  Inter-relations  of  the 
Main  Stems  and  Branches  of  the  Indo-Germanic  Languages  arc 
Analogous  to  the  Inter-relations  of  the  Main  Stems  and  Branches 
of  the  Vertebrate  Tribe. — The  Parent  Forms  in  both  Cases  are 
Extinct. — The  Most  Important  Stages  among  the  Human  An- 
cestral Forms. — Monera  originated  by  Spontaneous  Generation. 
— Necessity  of  Spontaneous  Generation 


VI  CONTENTS. 

CHAPTER  XVI. 

THE  ANCESTRY  OP  MAN. 
I.  From  the  Monera  to  the  Gasth^ea. 

PACR 

Relation  of  the  General  Inductive  Law  of  the  Theory  of  Descent  to 
the  Special  Deductive  Laws  of  the  Hypotheses  of  Descent. — Incom- 
pleteness of  the  Three  Great  Records  of  Creation :  Paleontology, 
Ontogeny,  and  Comparative  Anatomy. — Unequal  Certainty  of  the 
Various  Special  Hypotheses  of  Descent. — The  Ancestral  Line  of 
Men  in  Twenty-two  Stages  :  Eight  Invertebrate  and  Fourteen  Verte- 
brate Ancestors. — Distribution  of  these  Twenty-two  Parent-forms 
in  the  Five  Main  Divisions  of  the  Organic  History  of  the  Earth. — 
First  Ancestral  Stage  :  Monera. — The  Structureless  and  Homo- 
geneous Plasson  of  the  Monera. — Differentiation  of  the  Plasson 
into  Nucleus,  and  the  Protoplasm  of  the  Cells. — Cjtods  and  Cells 
as  Two  Different  Plastid-forms.— Vital  Phenomena  of  Monera. — 
Organisms  without  Organs. — Second  Ancestral  Stage  :  Amoebae. 
— One-celled  Primitive  Animals  of  the  Simplest  and  most  Uu- 
di  Keren  tiated  Nature. — The  Amoeboid  Egg-cells. — The  Egg  is  Older 
than  the  Hen. — Third  Ancestral  Stage  :  Syn-Amceba,  Ontogeneti- 
cally  reproduced  in  the  Morula. — A  Community  of  Homogeneous 
Amoeboid  Cells. — Fourth  Ancestral  Stage :  Planaea,  Ontogenetically 
reproduced  in  the  Blastula  or  Pianola. — Fifth  Ancestral  Stage: 
Gastraea,  Ontogenetically  reproduced  in  the  Gastrula  and  the  Two- 
layered  Germ-disc— Origin  of  the  Gastraia  by  Inversion  (invagi- 
natid)  of  the  Planaaa. — Haliphysema  and  Gastrophysema. — Extant 
Gastrajads  ...  ...  ...  ...  ...  ...     34 


CHAPTER  XVII. 

THE  ANCESTRAL  SERIES  OF  MAN. 
II.  From  the  Primitive  Worm  to  the  Skulled  Animal. 

The  Four  Higher  Animal  Tribes  are  descended  from  the  Worm  Tribe. 
— The  Descendants  of  the  Gastrsea ;  in  one  direction  the  Parent 
Form  of  Plant-Animals  (Sponges  and  Sea-Nettles),  in  the  other 
the  Parent  Form  of  Worms. — Radiate  form  of  the  former,  Bilateral 
form  of  the  latter. — The  Two  Main  Divisions  of  the  Worms, 
Accelomi  and  Ccelomati :  the  former  without,  the  latter  with,  a 
Body  Cavity  and  Blood-vessel  System. — Sixth  Ancestral  Stage  : 
Archeltninthes,  most  nearly  allied  to  Turbellaria. — Descent  of  the 


CONTENTS.  Vll 

PACE 

Coelomati  from  the  Acoelomi. — Mantled  Animals  (Tunicata)  and 
Chorda-Animals  (Chordoma).— Seventh  Stage:  Soft-Worms  (Scole- 
cida). — A  Sido  Branch  of  the  latter:  the  Acom-Worni  (Balano- 
glossus). — Differentiation  of  the  Intestinal  Tnbe  into  Gill-intes- 
tine and  Stomach-intestine. — Eighth  Stage  :  Chorda-Animak  (Chor- 
donia). — Ascidian  Larva  exhibits  the  Outline  of  a  Chorda-Animal. — 
Construction  of  the  Notochord. — Mantled  Animals  and  Verte- 
brates as  Diverging  Branches  of  Chorda-Animals. — Separation  of 
"Vertebrates  from  the  other  Higher  Animal  Tribes  (Articulated 
Animals,  Star-Animals,  Soft-bodied  Animals). — Significance  of  the 
Metameric  Formation. — Skull-less  Animals  (Acrania)  and  Skulled 
Animals  (Craniota). — Ninth  Ancestral  Stage  :  Skull-less  Animals. 
— Amphioxus  and  Primitive  Vertebrate. — Development  of  Skulled 
Animals  (Construction  of  the  Head,  Skull,  and  Brain). — Tenth 
Ancestral  Stage  :  Skulled  Animals,  allied  to  the  Cyclostomi  (Myxi- 
noidce  and  I'etromy zonidce)      ...  ...  ...  ...  ...     71 


CHAPTER  XVIII. 

THE   PEDIGREE   OF   MAN. 
III.  From  rajs  Primitive  Fish  to  the  Amniotic  Animal. 

Comparative  Anatomy  of  the  Vertebrates. — The  Characteristic  Qualities 
of  the  Double-nostrilled  and  Jaw-mouthed  :  the  Double-Nostrils, 
the  Gill-arch  Apparatus,  with  the  Jaw-arches,  the  Swimming- 
bladder,  the  Two  Pairs  of  Limbs. — Relationship  of  the  Three 
Groups  of  Fishes  :  the  Primitive  Fishes  (Selachii),  the  Ganoids 
(Ganoides),  the  Osseous  Fishes  (Teleostei). — Dawn  of  Terrestrial 
Life  on  the  Earth.—  Modification  of  the  Swimming-bladder  into 
the  Lungs. — Intermediate  Position  of  the  Dipnousta  between  the 
Primitive  Fishes  and  Amphibia.  —  The  Three  Extant  Dipneusta 
(Protopterus,  Lepidosiren,  Ceratodus). — Modification  of  the  Many- 
toed  Fin  of  the  Fish  into  the  Five-toed  Foot. — Causes  and  Effects 
of  the  latter. — Descent  of  all  Higher  Vertebrates  from  a  Five-toed 
Amphibian. — Intermediate  Position  of  the  Amphibians  between  the 
Lower  and  Higher  Vertebrates. — Modification  or  Metamorphosis  of 
Frogs. —  Different  Stages  in  .Amphibian  Metamorphosis. — The 
Gilled  Batrachians  (Proteus  and  Axolotl). — The  Tailed  Batrachians 
(Salamanders  and  Mud-fish). — Frog  Batrachians  (Frogs  and 
Toads). — Chief  Group  of  the  Amnion  Animals,  or  Amniota  (Reptiles, 
Birds,  and  Mammals). — Descent  of  all  the  Amniota  from  a  Common 


L  CONTENTS. 

PAGE 

Lizard-like  Parent-form  (Protamnion) . — First  Formation  of  the 
Allantois  and  of  the  Amnion. — Branching  of  the  Amnion  Animals 
in  Two  Lines  :  on  the  one  side,  Reptiles  (and  Birds),  on  the  other 
side,  Mammals         ...  ...  ...  ...  ...  ...  107 


CHAPTER  XIX. 

THE    PEDIGREE    OF   MAN. 
IV.    From  the  Primitive  Mammal  to  the  Ape. 

The  Mammalian  Character  of  Man. — Common  Descent  of  all  Mammals 
from  a  Single  Parent-form  (Promammalian). — Bifurcation  of  the 
Amnion  Animals  into  Two  Main  Lines :  on  the  one  side,  Eep- 
tiles and  Birds,  on  the  other,  Mammals. — Date  of  the  Origin  of 
Mammals  :  the  Trias  Period. — The  Three  Main  Groups  or  Sub- 
classes of  Mammals :  their  Genealogical  Belations. — Sixteenth 
Ancestral  Stage  :  Cloacal  Animals  (Monotremata,  or  Ornithodelpliia) . 
— The  Extinct  Primitive  Mammals  (Promammalia)  and  the  Extant 
Beaked  Animals  (Ovnithostoma) . — Seventeenth  Ancestral  Stage: 
Pouched  Animals  (Marsupialia,  or  DidelpJiia) . — Extinct  and  Extant 
Pouched  Animals. — Their  Intermediate  Position  between  Mono- 
trcmes  and  Placental  Animals. — Origin  and  Structure  of  Placental 
Animals  (Placentalia,  or  Monodelphia) . — Formation  of  the  Pla- 
centa.— The  Deciduous  Embryonic  Membrane  (Decidua). —  Group 
of  the  Indecidua  and  of  the  Deciduata. — The  Formation  of  the 
Decidua  (vera,  serotina,  refiexa)  in  Man  and  in  Apes. — Eighteenth 
Stage:  Semi-apes  (Prosimiw). — Nineteenth  Stage  :  Tailed  Apes 
(Menocerca). — Twentieth  Stage  :  Man-like  Apes  (Antliropoides). — 
Speechless  and  Speaking  Men  (Mali.  Homines)  ...  ...  140 


CHAPTER  XX. 

THE    HISTORY  OF  THE    EVOLUTION    OF   THE    EPIDERMIS   AND 
THE  NERVOUS  SYSTEM. 

Animal  and  Vegetative  Organ-systems  — Original  Relations  of  these  to 
the  Two  Primary  Germ-layers. —  Sensory  Apparatus. — Constituents 
of  Sensory  Apparatus :  originally  only  the  Exoderm,  or  Skin-layer; 
afterwards,  the  Skin-covering  specialized  from  the  Nerve-system. 
— Double  Function    of    the  Skin  (as  a  Covering  and  as    Organ  of 


CONTENTS.  IX 


Touch). — Outer  Skin  (Epidermis)  and  Leather-skin  (Corium). — 
Appendages  of  the  Epidermis  :  Skin-glauds  (Sweat-glands,  Tear- 
glands,  Sebaceous  Glands,  Milk-glands) ;  Nails  and  Hair.— The 
Embryonic  Wool-covering. — Hair  of  the  Head  and  of  the  Beard. — 
Influence  of  Sexual  Selection. — Arrangement  of  the  Nerve-system. 
— Motor  and  Sensory  Nerves. — Central  Marrow  :  Brain  and  Dorsal 
Marrow. — Constitution  of  the  Human  Brain  :  Large  Brain  (Cere- 
brum) and  Small  Brain  (Cerebellum). — Comparative  Anatomy  of 
the  Central  Marrow. — Germ-history  of  the  Medullary-tube. — Sepa- 
ration of  the  Medullary-tube  into  Brain  and  Dorsal  Marrow. — 
Modification  of  the  Simple  Brain-bladder  into  Five  Consecutive 
Brain-bladders :  Fore-brain  (Large  Brain,  or  Cerebrum),  Twixt- 
brain  ("Centre  of  Sight"),  Mid-brain  ("Four  Bulbs"),  Hind-brain 
(Small  Brain,  or  Cerebellum),  After-brain  (Neck  Medulla). — Various 
Formation  of  the  Five  Brain-bladders  in  the  various  Vertebrate 
Classes. — Development  of  the  Conductive  Marrow,  or  "Peripheric 
Nervous  System"    ...  ...  ...  ...  ...  ...  190 


CHAPTER  XXI. 

DEVELOPMENT   OF  THE   SENSE-ORGANS. 

Origin  of  the  most  highly  Purposive  Sense-organs  by  no  Preconceived 
Purpose,  but  simply  by  Natural  Selection. — The  Six  Sense-organs 
and  the  Seven  Sense-functions. — All  the  Sense-organs  originally 
Developed  from  the  Outer  Skin-covering  (from  the  Skin-sensory 
Layer). — Organs  of  the  Pressure  Sense,  the  Heat  Sense,  the 
Sexual  Sense,  and  the  Taste  Sense. — Structure  of  the  Organ  of 
Scent. — The  Blind  Nose-pits  of  Fishes. — The  Nasal  Furrows  change 
into  Nasal  Canals. — Separation  of  the  Cavities  of  the  Nose  and 
Mouth  by  the  Palate  Roof. — Structure  of  the  Eye. — The  Primary 
Eye  Vesicles  (Stalked  Protuberances  from  the  Twixt-brain). — 
Inversion  of  this  Eye  Vesicle  by  the  Crystalline  Lens,  separated 
from  the  Horn-plate. — Inversion  of  the  Vitreous  Body. — The  Vas. 
cular  Capsule  and  the  Fibrous  Capsule  of  the  Eyeball. — Eyelids. 
— Structure  of  the  Ear. — The  Apparatus  for  Perception  of  Sound  : 
Labyrinth  and  Auditory  Nerve. — Origin  of  the  Labyrinth  from 
the  Primitive  Ear  Vesicles  (by  Separation  from  the  Horn-plate). — 
Conducting  Apparatus  of  Sound  :  Drum  Cavity,  Ear  Bonelets,  and 
Drum  Membrane. — Origin  of  these  from  the  First  Gill-opening 
and  the  Parts  immediately  round  it  (the  First  and  Second  Gill- 
arch). — Rudimentary  Outer  Ear. — Rudimentary  Muscles  of  the 
Ear-shell  ...  ...  ...  ...  ...  ...  233 


X  CONTENTS. 

CHAPTER  XXII. 

DEVELOPMENT  OF  THE  ORGANS  OF  MOTION. 

PAGB 

The  Motive  Apparatus  of  Vertebrates. — These  are  constituted  by  the 
Passive  and  Active  Organs  of  Motion  (Skeleton  and  Muscles). — 
The  Significance  of  the  Internal  Skeleton  of  Vertebrates. — Struc- 
ture of  the  Vertebral  Column. — Formation  and  Number  of  the 
Vertebra?. — The  Ribs  and  Breast-bone. — Germ-history  of  the  Verte- 
bral Column. — The  Notochord. — The  Primitive  Vertebral  Plates. — 
The  Formation  of  the  Metamera. — Cartilaginous  and  Bony  Verte- 
bra?.— Intervertebral  Discs. — Head-skeleton  (Skull  and  Gill-arches). 
— Vertebral  Theory  of  the  Skull  (Goethe  and  Oken,  Huxley  and- 
Gegenbaur). — Primitive  Skull,  or  Primordial  Cranium. — Its  Forma- 
tion from  Nine  or  Ten  Coalescent  Metamera. — The  Gill-arches 
(Ribs  of  the  Head). — Bones  of  the  Two  Pairs  of  Limbs. — Develop- 
ment of  the  Five-toed  Foot,  adapted  for  Walking,  from  the  Many- 
toed  Fin  of  the  Fish. — The  Primitive  Fin  of  the  Selachians 
(Archipterygium  of  Gegenbaur). — Transition  of  the  Pinnate  into 
the  Semi-pinnate  Fin. — Atrophy  of  the  Rays  or  Toes  of  the  Fins. — 
Many-fingered  and  Five-fingered  Vertebrates. — Comparison  of  the 
Anterior  Limbs  (Pectoral  Fins)  and  the  Posterior  Limbs  (Ventral 
Fins). — Shoulder  Girdle  aud  Pelvis  Girdle. — Germ-history  of  the 
Limbs. — Development  of  the  Muscles  ...  ...  ...  273 

CHAPTER  XXIII. 

DEVELOPMENT  OF  THE  INTESTINAL  SYSTEM. 

The  Primitive  Intestine  of  the  Gastrula. — Its  Homology,  or  Morpho- 
logical Identity  in  all  Animals  (excepting  the  Protozoa). — Survey 
of  the  Structure  of  the  Developed  Intestinal  Canal  in  Man. — The 
Mouth-cavity. — The  Throat  (pharynx). — The  Gullet  (oesophagus). — 
The  Wind-pipe  (trachea)  and  Lungs. — The  Larynx. — The  Stomach. 
— The  Small  Intestine. — The  Liver  and  Gall-bladder. — The  Ventral 
Salivary  Gland  (pancreas). — The  Large  Intestine. — The  Rectum. — 
The  First  Rudiment  of  the  Simple  Intestinal  Tube. — The  Gastrula 
of  the  Amphioxus  aud  of  Mammals. — Separation  of  the  Germ  from 
the  Intestinal  Germ  Vesicle  (Gastrocystis). — The  Primitive  Intes- 
tine (Protogaster)  and  the  After  Intestine  (Metagaster) . — Secondary 
Formation  of  the  Mouth  and  Anus  from  the  Outer  Skiu. — Develop- 
ment of  the  Intestinal  Epithelium  from  the  Intestinal-glandular 
Layer,  and  of  all  other  parts  of  the  Intestine  from  the  Intestinal- 
fibrous  Layer. — Simple  Intestinal  Pouch   of  the  Lower  Worms. — 


CONTENTS.  XI 

PAGE 

Differentiation  of  the  Primitive  Intestinal  Tube  into  a  Respiratory 
and  a  Digestive  Intestine. — Gill-intestine  and  Stomach-intestine  of 
the  Amphioxus  and  Ascidian. — Origin  and  Significance  of  the  Gill- 
openings. — Their  Disappearance. — The  Gill-arches  and  the  Jaw- 
Skeleton. — Formation  of  the  Teeth. — Development  of  the  Langs 
from  the  Swim-bladder  of  Fish. — Differentiation  of  the  Stomach. — 
Development  of  the  Liver  and  Pancreas. — Differentiation  of  the 
Small  and  Large  Intestines. — Formation  of  the  Cloaca    ...  ...  311 

CHAPTER  XXIV. 

DEVELOPMENT  OF  THE  VASCULAR  SYSTEM. 

Application  of  the  Fundamental  Law  of  Biogeny. — The  Two  Sides. — 
Heredity  of  Conservative  Organs. — Adaptation  of  Progressive 
Organs. — Ontogeny  and  Comparative  Anatomy  complementary  of 
each  other. — New  "  Theories  of  Evolution  "  of  His. — The  "  En- 
velope Theory  "  and  the  "  Waste-rag  Theory." — Main  Germ  and 
Supplementary  Germ. — Formative  Yelk  and  Nutritive  Yelk. — Phy- 
looenetic  Origin  of  the  latter  from  the  Primitive  Intestine.— Origin 
of  the  Vascular  System  from  the  Vascular  Layer,  or  Intestinal- 
fibrous  Layer. — Phylogenetic  Significance  of  the  Ontogenetic  Suc- 
cession of  the  Organ-systems  and  Tissues. — Deviation  from  the 
Original  Sequence  ;  Ontogenetic  Heterochronism. — Covering  Tissue. 
— Connective  Tissue. — Nerve-muscle  Tissue. — Vascular  Tissue. — 
Relative  Age  of  the  Vascular  System. — First  Commencement  of 
the  Latter ;  Coeloma. — Dorsal  Vessel  and  Ventral  Vessel  of  Worms. 
— Simple  Heart  of  Ascidia. — Atrophy  of  the  Heart  in  the  Am- 
phioxus.— Two-chambered  Heart  of  the  Cyclostoma. — Arterial 
Arches  of  the  Solachii. — Double  Auricle  in  Dipneusta  and  Am- 
phibia.— Double  Ventricle  in  Birds  and  Mammals. — Arterial  Arches 
in  Birds  and  Mammals. — Germ-history  (Ontogeny)  of  the  Human 
Heart. — Parallelism  of  the  Tribal-history  (Phylogcny)     ...  ...   318 

CHAPTER  XXV. 

DEVELOPMENT  OF  THE  URINARY  AND  SEXUAL  ORGANS. 

Importance  of  Reproduction. — Growth. — Simplest  Forms  of  Asexual 
Reproduct  inn  :  Division  and  the  Formation  of  Buds  (Gemmation). — 
Simplest  Forms  of  Sexual  Reproduction:  Amalgamation  of  Two 
Differentiated  Cells;  the  Male  Sperm-cell  and  the  Female  Egg-cell. 

— Fertilization.— Source    of     Love. — Original     Hermaphroditism; 


XII  CONTENTS. 

PACE 

Later  Separation  of  the  Sexes  (Gonochorism).— Original  Develop- 
ment of  the  Two  Kinds  of  Sexual  Cells  from  the  Two  Primary 
Germ-layers. — The  Male  Exoderm  and  Female  Entoderm. — Develop- 
ment of  the  Testes  and  Ovaries. — Passage  of  the  Sexual  Cells  into 
the  Ccelom. — Hermaphrodite  Rudiment  of  the  Embryonic  Epi- 
thelium, or  Sexual  Plate. — Channels  of  Exit,  or  Sexual  Ducts. — 
Egg-duct  and  Seed-duct. — Development  of  these  from  the  Primitive 
Kidney  Ducts. — Excretory  Organs  of  worms. — "  Coiled  Canals  "  of 
Ringed  Worms  {Annelida). — Side  Canals  of  the  Amphioxus. — 
Primitive  Kidneys  of  the  Myxinoides. — Primitive  Kidneys  of  Skulled 
Animals  (Craniota). — Development  of  the  Permanent  Secondary 
Kidneys  in  Amniota. — Development  of  the  Urinary  Bladder  from 
the  Allantois. — Differentiation  of  the  Primary  and  Secondary 
Primitive  Kidney  Ducts. — The  Miillerian  Duct  (Egg-duct)  and  the 
Wolffian  Duct  (Seed-duct). — Change  of  Position  of  the  Germ-glands 
in  Mammals.— Formation  of  the  Egg  in  Mammals  (Graafian  Fol- 
licle).— Origin  of  the  External  Sexual  Organs. — Formation  of  the 
Cloaca. — Hermaphroditism  in  Man      ...  ...  ...  ...  388 

CHAPTER  XXVI. 

RESULTS  OF  ANTHROPOGENY. 

Review  of  the  Germ-history  as  given. — Its  Explanation  by  the  Funda- 
mental Law  of  Biogeny. — Its  Causal  Relation  to  the  History  of  the 
Tribe. — Rudimentary  Organs  of  Man. — Dysteleology,  or  the  Doc- 
trine of  Purposelessness. — Inheritances  from  Apes.— Man's  jriace  in 
the  Natural  System  of  the  Animal  Kingdom. — Man  as  a  Vertebrate 
and  a  Mammal. — Special  Tribal  Relation  of  Men  and  Apes. — 
Evidences  regarding  the  Ape  Question. — The  Catarhina  and  the 
Platyrhina. — The  Divine  Origin  of  Man. — Adam  and  Eve. — History 
of  the  Evolution  of  the  Mind. — Important  Mental  Differences  within 
a  Single  Class  of  Animals. — The  Mammalian  Mind  and  the  Insect 
Mind. — Mind  in  the  Ant  and  in  the  Scale-louse  (Coccus). — Mind  in 
Man  and  in  Ape. — The  Organ  of  Mental  Activity  :  the  Central 
Nervous  System. — The  Ontogeny  and  Phylogeny  of  the  Mind. — 
The  Monistic  aud  Dualistic  Theories  of  the  Mind. — Heredity  of  the 
Mind. — Bearing  of  the  Fundamental  Law  of  Biogeny  on  Psychology. 
— Influence  of  Anthropogeny  on  the  Victory  of  the  Monistic  Philo- 
sophy and  the  Defeat  of  the  Dualistic. — Nature  and  Spirit. — Natural 
Science  and  Spiritual  Science. — Conception  of  the  World  reformed 
by  Anthropogeny     ...  ...  ...  ...  ...  ...  432 

Notes.    Remarks  and  References  to  Literature  ...  ...     459 

Index  ...  ...  ...  ...  ...  ...  491 


LIST   OF   PLATES. 


Plate  XII.  (between  p.  130  and  p.  131).  The  Australian  Mud- 
fish (Ceratodus  Foster i)        ...  ...  ...     Explanation     118 

Plate  XIII.  (between  p.  130  and  p.  131).  The  Mexican  Axolotl 
(Siredon  pisciformis)  and  the  European  Land-salamander 
(Scdamandra  maculata)         ...  ...  ...     Explanation     129 

Plate    XIV.    (between  p.  180  and  p.  181).      Four  Catarhines 

(Chimpanzee,  Gorilla,  Orang,  Negro)  ...     Explanation     181 

Tlate  XV.  (between  p.  188  and  p.  189).     Pedigree  of  Man 

Explanation     184 


LIST   OF   WOODCUTS. 


PAGE 
46 

49 
51 
51 
53 
53 
55 
55 
57 
60 


163.  Moneron  (Protamosha) 

164.  Bathybius,  primitive  slime 

165.  Monerula  of  Mammal 

166.  Cytula  of  Mammal  . 

167.  Amoeba    .... 

168.  Amoeboid  egg-cell    . 

169.  Original  egg-cleavage 

170.  Mulberry-germ  (Morula) . 

171.  Germination  of  Monoxenia 

172.  173.  Magosphaera      . 
174-179.  Gastrula   of   various 

animals  .  .65 

180,  181.  Halipbysema    .  .       67 

182,  183.  Ascula  of  a  Sponge  .       68 
184,  185.  A       Gliding- worm 

(Rhabdocoelum)       .  .       80 

186.  Acorn-worm   (Balanoglos- 

sus)        ....       86 

187.  Appendicularia         .         .90 

188.  Ascidia     .         .  90 

189.  Ampbioxus       ...       91 

190.  Lamprey  (Petromyson)     .     103 

191.  192.   Shark    (Selachii)      .     113 

193.  Larval  Salamander  .         .     127 

194.  Larval  Frog  (Tadpole)     .     127 


FIGURE  PAGE 

195,  196.  Beaked  Animal  (Orni- 
tliorhynchuif)  and  its 
skeleton         .         .         .     148 

197.  Pouched  Animal  (Marsu- 

pial) with  young    .         .     152 

198.  Human  egg-membranes    .     158 

199.  Semi-ape  (Lori)       .  .161 

200.  Human    germ    with     its 

membranes    .         .         .     166 

201.  Human  uterus,  navel-cord, 

and  embryo  .         .  .  167 

202.  Head  of  Nose-ape     .  .  175 

203.  Tailed  Ape  (Sea-cat)  .  175 
20  k  Skeleton  of  Gibbon  .  178 

205.  Skeleton  of  Orang-outang  178 

206.  Skeleton  of  Chimpanzee  .  178 

207.  Skeleton  of  Gorilla  .         .  178 

208.  Skeleton  of  Man       .         .  178 

209.  Gastrula    of     Gastrophy- 

sema      ....     198 

210.  Germ-layers     of     Earth- 

worms .         .         .     198 

211.  Nerve-system  of  Gliding- 

worm     ....     19S 
212    Human  skin-covering       .     200 


LIST    OF   WOODCUTS. 


XV 


PIGDKB 

PAGE 

213.  Epidermis  cells         . 

201 

214.  Tear-glands      . 

202 

215,  216.  Milk-glands      . 

203 

217,  218.   Central    marrow    of 

human  embryo 

210 

219.  Human  brain    . 

212 

220.          „           

213 

221-223.  Lyre-shaped  embryo 

Chick     .... 

218 

221-226.  The   five   brain-blad- 

ders of  the  human  germ 

220 

227.  The  five  brain-bladders  of 

Craniota         .         .         . 

222 

228.  Brain  of  Shark 

222 

229.  Brain  of  Frog  . 

222 

230.  Brain  of  Babbit 

224 

231.  Nose  of  Shark 

241 

232-236.  Development   of  the 

face  in  embryo  Chick    . 

243 

237.  Nose  and  month  cavities  . 

246 

238-240.  The     face      in     the 

human  embryo       .         . 

247 

211.  Human  eye 

250 

212.  Development  of  tbe  eyes 

253 

213. 

256 

214.  Human  auditory  passage 

260 

245.  Human  auditory  labyrinth 

263 

246-248.  Development  of  the 

ear         .... 

264 

249.  Primitive  skull  with  ear- 

vesicles 

264 

250.  Budimentary  ear-muscles 

270 

251,  252.  Human  skeleton 

279 

253.  Human  vertebral  column 

280 

254.  Neck-vertebra          .         . 

281 

255.   Breast-vertebra        . 

281 

256.  Lumbar-vertebra 

2S1 

FtGUP.E  TACE 

257.  Portion  of  notochord         .  286 
258-260.  Growth  of  tbe  primi- 
tive vertebral  scries  in 

embryo  Chick         .          .  288 

261.  Longitudinal    section    of 

breast-vertebra      .         .  290 

262.  Transverse  section  of  same  291 

263.  Intervertebral  disc  .         .  291 

264.  Human  skull    .         .         .292 

265.  Head  skeleton  of  Primi- 

tive Fish        .         .         .296 

266.  Primitive  skull  of  Man    .  297 

267.  Skeleton  of  fin  of  Ceratodus  302 

268.  Skeleton  of  fin  of  Acan- 

thias      .        .         .         .302 

269.  Skeleton  of  fin  of  Primi- 

tive Fish        .         .         .302 

270.  Skeleton  of  hand  of  Frog  302 

271.  Skeletonof  hand  of  Gorilla  302 

272.  Skeleton  of  human  hand  .  302 

273.  Skeleton  of  hand  of  Mam- 

mal        .         .         .         .  306 

274.  Gastrula  of  Ohjnthus       .  313 

275.  Human  stomach       .         ,  317 

276.  Gastrula  of  Amphioxus    .  321 

277.  Gastrula  of  Mammal         .  321 

278.  279.  Human    germ    with 

yelk-sac  and  allantois   .  '324 

280.  Intestine  of  Turbellaria  .  327 

281.  Intestine  of  Ascidia           .  327 

282.  Intestine  of  Amphioxus    .  328 

283.  Scales  of  Shark        .         .  332 

284.  285.  Intestine  of  embryo 

Dog  with  the  intestinal 

glands   ....  334 

286.  Intestine  with  allantois    .  338 

287.  Intestine  of  human  germ  339 


XVI 


LIST   OF   WOODCUTS. 


FIGURE 

288.  Liver  of  human  germ 

289.  Nail-tissue 

290.  Intestinal  epithelium 

291.  Jelly-like  tissue 

292.  Cartilaginous  tissue 

293.  Neuro-uiuscular  cells 

294.  Nerve-tissue     . 

295.  Muscle-tissue   .         . 

296.  Vascular  tissue 

297.  Blood-cells 

298.  Blood-vessels  of  a  Worm  . 

299.  Head  with  blood-vessels 

of  Fish  .... 
300-302.  Arterial  arches 
303-306.         „  „ 

307-310.  Development    of  the 

heart      .... 
311-314.  Development  of  the 

heart     .... 
315.  Transverse         section 

through  Haliphysema    . 


PAGE 

FIG  UltF. 

PACE 

342 

316. 

Rudiments  of  Urogenitalia 

400 

362 

317. 

Primitive  kidney  of  Bdello- 

362 

stoma    .... 

406 

363 

318. 

Earliest  primitive  kidney 

363 

rudiments 

408 

364 

319, 

320.  Primitive  kidneys  of 

364 

Mammals 

409 

364 

321. 

Development  of  urogeni- 

365 

tal  system      .         . 

414 

365 

322, 

323.         „                  „ 

415 

371 

324- 

326. 

416 

327. 

Female    sexual  organs  of 

375 

Beaked    Animal    (Orni- 

377 

thorhynchus) 

418 

378 

328. 

Change  of  position  of  both 
kinds    of  sexual  glands 

380 

in  human  beings   . 

420 

329. 

Development  of  the  human 

382 

external   sexual    organs 

422 

330. 

Human  egg-follicles 

426 

393 

LIST   OF   GENETIC  TABLES. 


TABLE 

XII.     Systematic  Survey  of  paloeontological  periods 

XIII.  Systematic  Survey  of  paloeontological  formations     ... 

XIV.  Systematic   Survey  of  the  thickness   of  the   forma- 

tions 
XV.     Pedigree  of  Indo-Germanic  languages 
XVI.     Systematic  Survey  of  the  most  important  stages  in 

the  animal  ancestral  line  of  Man 
XVII.     Systematic   Survey   of   the   five   first   stages   in  the 
evolution  of  Man  (phylogenetic,  ontogenetic,  sys- 
tematic) 
XVIII.     Systematic  Survey  of  the  phylogenetic  system  of  the 
animal  kingdom 
XIX.     Monophyletic  pedigree  of  the  animal  kingdom 
XX.     Systematic   Survey   of   the   phylogenetic   system   of 

Vertebrates... 
XXI.     Monophyletic  pedigree  of  Vertebrates 
XXII.     Systematic   Survey  of   the  periods  of   human  tribal 
history 

XXIII.  Systematic   Survey   of   the   phylogenetic   system   of 

Mammals,  founded  on  the  Gastnea  Theory 

XXIV.  Monophyletic  pedigree  of  Mammals 
XXV.     Pedigree  of  Apes 

XXVI.     Systematic  Survey  of  the  organ-systems  of  the  human 

body 

XXVII.     Systematic  Survey  of  the  phylogenetic  history  of  the 

human  skin-covering 
XXVIII.     Systematic  Survey  of  the  phylogenetic  history  of  the 
human  nerve-system 


11 
12 

19 
23 

44 


70 

92 
93 

120 
121 

184 

187 
188 
189 

194 

229 

230 


XV111  LIST   OF   GENETIC   TABLES. 

TABLE  PAGB 

XXIX.     Systematic  Survey  of  the  ontogeny  of  the  skin  and 

nerve  systems  ...  ...  ...  ...     232 

XXX.     Systematic  Survey  of  the  phylogeny  of  the  human 

nose  ...  ...  ...  ...  ...     249 

XXXI.     Systematic  Survey  of  the  ontogeny  of  the  human 

eye  ...  ...  ...  ...  ...     258 

XXXII.     Systematic  Survey  of  the  phylogeny  of  the  human 

ear  ...  ...  ...  ...  ...     267 

XXXIII.  Systematic  Survey  of  the  ontogeny  of  the  human 

ear  ...  ...  ...  ...  ...     208 

XXXIV.  Systematic  Survey  of  the  constitution  of  the  human 

skeleton     ...  ...  ...  ...  ...     278 

XXXV.     Systematic  Survey  of  the  phylogeny  of  the  human 

skeleton     ...  ...  ...  ...  309 

XXXVI.     Systematic  Survey  of  the  constitution  of  the  human 

intestinal  system      ...  ...  ...  ...     330 

XXXVII.     Systematic  Survey  of  the  phylogeny  of  the  human 

intestinal  system      ...  ...  ...  ...     340 

XXXVIII.     Systematic   Survey  of  the  sequence,  according  to 
age,  of   the  human  tissue-groups  (phylogenetic 
sequence  of  the  tissues)  ...  ...  ...     300 

XXXIX.     Systematic   Survey  of  the  sequence,  according  to 
age,  of  the  human  organ-systems  (phylogenetic 
sequence  of  the  organs)  ...  ...  ...     307 

XL.     Systematic  Survey  of  the  phylogeny  of  the  human 

vascular  system        ...  ...  ...  ...     384 

XLI.     Systematic  Survey  of  the  phylogeny  of  the  human 

heart  ...    '         ...  ...    '        ...  ...     385 

XLII.     Systematic  Survey  of   the  homologies  of  Worms, 
Articulated   Animals  {Arthropoda),    Soft-bodied 
Animals  (Mollusca),  and  Vertebrates  ...  ...     387 

XLIII.     Systematic  Survey  of  the  phylogeny  of  the  human 

urinary  and  sexual  organs      ...  ...  ...     428 

XLIV.     Systematic  Survey  of  the  homologies  of  the  sexual 

organs  in  the  two  sexes  of  Mammals  ...  ...     431 


TIIE  EVOLUTION  OF  MAN. 

CHAPTER  XV. 

THE   DURATION   OF   HUMAN   TRTBAL   HISTORY. 

Comparison  of  Ontogenetic  and  Phylogenetic  Periods  of  Time. — Duration  of 
Germ-history  in  Man  and  in  Different  Animals. — Extreme  Brevity  of 
tbe  Latter  in  Comparison  with  the  Immeasurable  Long  Periods  of 
Tribal  History. — Kelation  of  this  Rapid  Ontogenetic  Modification  to  the 
Slow  Pbylogenetic  Metamorphosis. — Estimate  of  the  Past  Duration  of 
the  Organic  World,  founded  on  the  Relative  Thickness  of  Sedimentary 
Rock-strata,  or  Neptunian  Formations. — The  Five  Main  Divisions  in 
the  Latter :  I.  Primordial,  or  Archilithic  Epoch.  II.  Primary,  or 
Palaeolithic  Epoch.  III.  Secondary,  or  Mesolithic  Epoch.  IV.  Tertiary, 
or  Camolithic  Epoch.  V.  Quaternary,  or  Anthropolithic  Epoch. — The 
Relative  Duration  of  the  Five  Epochs.— The  Results  of  Comparative 
Philology  as  Explaining  the  Phylogeny  of  Species. — The  Inter-relations 
of  the  Main  Stems  and  Brandies  of  the  Indo-Germanic  Languages  are 
Analogous  to  the  Inter-relations  of  the  Main  Stems  and  Branches  of 
the  Vertebrate  Tribe. — The  Parent  Forms  in  both  Cases  are  Extinct.  — 
The  Most  Important  Stages  among  the  Human  Ancestral  Forms. — 
Moncra  originated  by  Spontaneous  Generation. — Necessity  of  Sponta- 
neous Generation. 

"In  vain  as  yet  has  it  been  attempted  to  draw  an  exact  line  of  demarcation 
between  historic  and  prehistoric  times;  the  origin  of  man  and  the  period  of 
his  first  appearance  pass  back  into  indefinable  time ;  the  so-called  archaic 
ago  cannot  be  sharply  distinguished  from  the  present  age.  This  is  the  fate 
of  all  geological,  as  of  all  historical  periods.  The  periods  which  we  dis- 
tinguish arc,  therefore,  mure  or  less  arbitrarily  defined,  and,  like  the  divisions 


2  THE   EVOLUTION   OF  MAN. 

in  systematic  natural  history,  can  only  serve  to  bring  the  subject  of  our 
study  better  before  us  and  to  render  it  more  manageable ;  but  not  to  mark 
real  distinctions  between  different  things." — Bernhard  Cotta  (1866). 

Our  comparative  study  of  the  Anatomy  and  Ontogeny  of 
the  Amphioxus  and  the  Ascidian  has  afforded  us  aid,  the 
value  of  which  can  hardly  be  over-estimated,  towards 
acquiring  a  knowledge  of  human  Ontogeny.  For  in  the 
first  place  we  have  in  this  way  filled  up,  as  regards  Anatomy, 
the  wide  chasm  which  in  all  previous  systems  of  the 
animal  kingdom  existed  between  Vertebrates  and  Inverte- 
brates ;  and  in  the  second  place,  in  the  germ-history  of  the 
Amphioxus  we  have  recognized  primordial  phases  of  de- 
velopment, which  have  long  disappeared  from  the  Ontogeny 
of  Man,  and  which  have  been  lost  in  accordance  with  the 
law  of  abridged  heredity.  Of  special  importance  among 
these  phases  of  development  is  the  Archigastrula,  the  ori- 
ginal, genuine  Gastrula-form  which  the  Amphioxus  has 
retained  up  to  ihe  present  time,  and  which  re-appears  in 
the  same  form  in  low  invertebrate  animals  of  the  most 
diverse  classes. 

The  germ-history  of  the  Amphioxus  and  the  Ascidian 
has,  therefore,  so  far  perfected  our  direct  knowledge  of 
human  genealogy,  that,  notwithstanding  the  incompleteness 
of  our  empiric  knowledge,  there  is  no  essential  gaj)  of  any- 
great  moment  in  the  pedigree.  We  may,  therefore,  at  once 
proceed  to  our  task,  and,  aided  by  the  ontogenetic  and 
comparative -anatomical  materials  at  our  command,  may 
reconstruct  the  main  outlines  of  human  Phylogeny.  The 
immense  importance  of  the  direct  application  of  the  funda- 
mental biogenetic  law  of  the  causal  connection  between 
Ontogeny  and  Phylogeny  now  becomes  evident.    But,  before 


TIME  KEQUIRED   FOR   THE   DEVELOPMENT   OF   MAN.  3 

beginning  this  task,  it  will  be  well  to  note  a  few  other 
general  facts  which  may  enable  us  better  to  understand  the 
phenomena  we  are  about  to  study. 

Firstly,  it  may  not  be  out  of  place  to  insert  a  few 
remarks  as  to  the  duration  of  time  during  which  Man  was 
developing  from  the  animal  kingdom.  The  first  thought 
that  occurs  to  the  mind  when  we  consider  the  facts  in 
question,  is  of  the  immense  difference  between  the  duration 
of  the  germ-history  of  Man  on  the  one  hand,  and  of  his 
tribal  history  on  the  other.  The  brief  period  in  which  the 
Ontogeny  of  the  human  individual  takes  place,  bears  no 
proportion  to  the  infinitely  long  period  required  for  the 
Phylogeny  of  the  human  tribe.  The  human  individual 
requires  nine  months  for  its  perfect  development  from  the 
fertilized  egg-cell  to  the  moment  at  which  it  is  born  and 
quits  the  mother's  body.  The  human  embryo,  therefore, 
passes  through  the  whole  course  of  its  development  in  the 
brief  space  of  40  weeks  (usually  in  exactly  280  days). 
Each  man  is  really  older  by  this  period  than  is  usually 
assumed.  When,  for  example,  a  child  is  said  to  be  9j  years 
old,  he  is  in  reality  10  years  old.  For  individual  existence 
does  not  begin  at  the  moment  of  birth,  but  at  the 
moment  of  fertilization.  In  many  other  Mammals  the 
duration  of  the  embryonic  development  is  the  same  as  in 
Man,  e.g.,  the  Ox.  In  the  Horse  and  the  Ass  it  is  somewhat 
loDger,  viz.,  from  43  to  45  weeks;  in  the  Camel  it  is  13 
months.  In  the  largest  Mammals  the  embryo  requires  a 
much  longer  time  for  its  complete  formation  within  the 
maternal  body;  in  the  Rhinoceros,  for  instance,  l£  year, 
in  the  Elephant  90  weeks.  In  the  latter  case,  therefore, 
gestation   lasts  more   than  twice  as  long  as  in  Man — for 


4  THE   EVOLUTION    OF   MAN. 

nearly  a  year  and  three  quarters.  In  the  smaller  Mammals, 
the  duration  of  embryonic  development  is,  on  the  contrary, 
much  shorter.  The  smallest  Mammals,  the  Harvest  Mice, 
develop  fully  in  3  weeks  ;  Rabbits  and  Hares  in  4  weeks ; 
Rats  and  Marmots  in  5  weeks  ;  the  Dog  in  9,  the  Pig  in  17, 
the  Sheep  in  21,  and  the  Stag  in  36  weeks.  Development  is 
yet  more  rapid  in  Birds.  The  Chick,  under  normal  con- 
ditions of  incubation,  requires  only  3  weeks,  or  just  21  days 
for  its  full  development.  The  Duck,  on  the  other  hand, 
takes  25,  the  Turkey  27,  the  Peacock  31,  the  Swan  42,  and 
the  New  Holland  Cassowary  65  days.  The  smallest  of  all 
Birds,  the  Humming-bird,  quits  the  egg  after  the  twelfth  day. 
It  is,  therefore,  evident  that  in  Mammals  and  in  Birds  the 
duration  of  development  within  the  egg-membranes  stands 
in  a  definite  relation  to  the  size  of  body  attained  by  each 
vertebrate  species.  But  the  latter  is  not  the  sole  determin- 
ing cause  of  the  former.  There  are  many  other  circum- 
stances which  influence  the  duration  of  individual  develop- 
ment within  the  membranes  of  the  egg.126 

In  all  cases,  however,  the  duration  of  the  Ontogeny 
appears  infinitely  brief  when  compared  with  the  enormous, 
the  infinitely  long  period  during  which  the  Phylogeny,  or 
gradual  development  of  the  ancestral  series,  took  place. 
This  period  is  not  to  be  measured  by  years  and  centuries, 
but  by  thousands  and  millions  of  years.  Many  millions  of 
years  must  indeed  have  elapsed  while  the  most  perfect 
vertebrate  organism,  Man,  gradually  developed  from  the 
primaeval  one-celled  ancestral  organism.  The  opponents  of 
the  development  theory,  who  regard  this  gradual  develop- 
ment of  Man  from  lower  animal  forms,  and  his  original 
descent  from  a  one-celled  primitive  animal  as  incredible, 


DURATION    OF   HUMAN    GERM-HISTORY.  5 

do  not  reflect  that  the  very  same  marvel  actually  recurs 
before  our  eyes  in  the  short  space  of  nine  months  during 
the  embryonic  development  of  each  human  individual. 
The  same  series  of  multifariously  diverse  forms,  through 
which  our  brute  ancestors  passed  in  the  course  of  many 
millions  of  years,  has  been  traversed  by  every  Man  during 
the  first  40  weeks  of  his  individual  existence  within  the 
maternal  body. 

All  changes  in  organic  forms,  all  metamorphoses  of 
animal  and  plant  forms,  appear  to  us  all  the  more  remark- 
able and  all  the  more  wonderful  in  proportion  as  they  occur 
more  rapidly.  When,  therefore,  our  opponents  pronounce  that 
the  past  development  of  the  human  race  from  lower  animal 
forms  is  incredible,  they  must  regard  the  embryonic  develop- 
ment of  the  human  individual  from  the  simple  egg-cell  as 
far  more  wonderful  in  comparison.  This  latter  process— the 
ontogenetic  modification — which  takes  place  before  our  eyes, 
must  appear  more  wonderful  than  the  phylogenetic  modifi- 
cation, in  proportion  as  the  duration  of  the  tribal  history 
exceeds  that  of  the  germ-history.  For  the  human  embryo 
must  pass  through  the  whole  process  of  individual  develop- 
ment, from  the  simple  cell  up  to  the  many-celled  perfect 
Man,  with  all  his  organs,  in  the  brief  space  of  40  weeks.  On 
the  other  hand,  we  may  assign  many  millions  of  years  for 
the  accomplishment  of  the  analogous  process  of  phyloge- 
netic development — the  development  of  Man's  ancestors  from 
the  simplest  one-celled  form. 

As  regards  these  phylogenetic  periods,  it  is  impossible 
to  fix  approximately  their  length  in  hundreds  or  in  thousands 
of  years,  or  to  establish  any  absolute  measure  of  their 
duration     But  the  researches  of  <reolo<nsts  have  louo-  since 


6  THE   EVOLUTION    OF   MAX. 

enabled  us  to  estimate  and  compare  the  relative  durations 
of  the  various  periods  of  the  earth's  organic  history.  The 
most  direct  standard  for  determining  the  relative  duration 
of  geological  peiiods  is  afforded  by  the  thickness  of  the  so- 
called  Neptunian  strata  or  sedimentary  rock,  i.e.,  all  those 
strata  "which  have  been  deposited,  as  mud,  at  the  bottom 
of  the  ocean,  or  under  fresh  water.  These  stratified  sedi- 
mentary rocks — limestone,  clay,  marl,  sandstone,  slate,  etc. — 
which  constitute  the  great  mass  of  mountain-chains,  and 
which  are  often  several  thousand  feet  in  thickness,  afford 
us  data  for  estimating  the  relative  lengths  of  the  various 
periods  of  the  earth's  history. 

For  the  sake  of  completeness,  I  must  say  a  few  words  as 
to  the  development  of  the  earth  as  a  whole,  briefly  indicating 
a  few  of  the  more  prominent  facts  relating  to  this  matter. 
At  the  very  outset  we  are  confronted  with  the  weighty 
fact,  that  life  originated  on  our  planet  at  a  certain  definite 
period.  This  is  a  proposition  that  is  no  longer  gainsaid  by 
any  competent  geologist.  We  now  know  for  certain  that 
organic  life  upon  our  planet  actually  began  at  a  certain 
time,  and  that  it  did  not  exist  there  from  eternity,  as 
some  have  supposed.  The  indisputable  proofs  of  this  are 
furnished,  on  the  one  hand,  by  physico-astronomical  cos- 
mogeny ;  on  the  other,  by  the  Ontogeny  of  organisms.  Species 
and  tribes,  like  individuals,  do  not  enjoy  a  perpetual 
life.127  They  also  had  a  beginning.  The  time  which  has 
elapsed  since  the  origin  of  life  upon  the  earth  up  to  the 
present  time  (and  with  this  period  of  time  alone  we  are 
here  concerned)  we  call  the  "  history  of  the  organic  earth," 
as  distinguished  from  the  "history  of  the  inorganic  earth" 
which  embraces  the  period  before  the  origin  of  organic  life. 


THE   FIRST   DEVELOPMENT  OF  ORGANIC   LIFE.  7 

With  regard  to  tlie  latter,  we  first  obtained  clear  ideas  from 
the  natural  philosophical  researches  and  computations  of 
the  great  critical  philosopher,  Immanuel  Kant,  and  on  this 
point  I  must  refer  the  reader  to  Kant's  "  Allgemeine  Natur- 
geschichte  und  Theorie  des  Himmels  "  and  to  the  numerous 
Cosmogenies  which  treat  the  subject  in  a  popular  style. 
We  cannot  here  dwell  upon  questions  of  this  kind. 

The  organic  history  of  the  earth  could  begin  only  when 
water  in  fluid  drops  existed  upon  its  surface.  For  the  very 
existence  of  all  organisms,  without  any  exception,  depends 
on  water  in  the  fluid  state,  their  bodies  containing  a  con- 
siderable amount  of  the  same.  Our  own  body,  in  its  fully 
developed  state,  contains  in  its  tissues  70  per  cent,  of  water 
and  only  30  per  cent,  of  solid  matter.  The  amount  of  water 
is  still  greater  in  the  body  of  the  child,  and  is  greatest  of  all 
in  the  embryo.  In  early  stages  of  development  the  human 
embryo  contains  more  than  90  per  cent,  of  water,  and  not 
10  per  cent,  of  solid  matter.  In  low  marine  animals, 
especially  in  the  Medusa?,  the  body  contains  even  more  than 
0!)  per  cent,  of  water,  and  not  even  one  per  cent,  of  solid 
matter.  No  organism  can  exist  and  perform  its  vital 
functions  without  water.     Without  water  there  is  no  life. 

Water  in  the  fluid  state,  which  is,  therefore,  in- 
dispensable for  the  existence  of  life,  could  not,  however, 
appear  upon  the  earth  until  after  the  temperature  of  the 
surface  of  the  fiery  globe  had  sunk  to  a  certain  point. 
Before  this  it  existed  only  in  the  form  of  steam.  As 
soon,  however,  as  the  first  drop  of  water  in  a  fluid  state  was 
precipitated  by  cooling  from  the  envelope  of  steam,  it  began 
its   geological   action,  and  from    that  time  to   this   it  has 

effected  continual  changes  in  the  modification  of  the  hard 
24 


8  THE    EVOLUTION   OF   MAN. 

crust  of  the  earth.  The  result  of  this  unceasing  work  of 
the  water,  which  in  the  form  of  rain  and  hail,  of  snow  and 
ice,  of  rushing  torrent  and  surging  wave  crumbles  and  dis- 
solves the  rocks,  is  the  formation  of  ooze.  As  Huxley  says, 
in  his  excellent  "Lectures  on  the  Causes  of  the  Phenomena  of 
Organic  Nature,"  the  most  important  fact  in  the  past  history 
of  our  earth  is  ooze,  and  the  question  as  to  the  history  of  the 
past  ages  of  the  world  resolves  itself  into  a  question  as  to 
the  formation  of  ooze.  AH  the  stratified  rocks  of  our  moun- 
tainous formations  were  originally  deposited  as  ooze  at  the 
bottom  of  the  waters,  and  only  afterwards  hardened  into 
solid  stone. 

As  has  already  been  said,  it  is  possible,  by  bringing 
together  and  comparing  the  various  rock-strata  from  many 
places  on  the  surface  of  the  earth,  to  obtain  an  approximate 
conception  of  the  relative  ages  of  these  various  strata. 
Geologists  have  long  agreed  that  there  is  an  entirely  definite 
historical  sequence  of  the  various  formations.  The  various 
groups  of  strata  which  lie  one  over  another  correspond  to 
successive  periods  in  the  earth's  organic  history,  during 
which  they  were  deposited  in  the  shape  of  mud  at  the 
bottom  of  the  sea.  Gradually  this  mud  was  hardened  into 
solid  rock.  The  latter,  by  alternate  upheaval  and  depres- 
sion of  the  surface  of  the  earth,  was  lifted  above  the  water, 
and  assumed  the  form  of  mountains.  Four  or  five  main 
periods  in  the  earth's  organic  history,  answering  to  the 
larger  and  smaller  groups  of  these  sedimentary  rock-strata, 
are  usually  distinguished.  These  main  periods  are  sub- 
divided into  numerous  subordinate  or  lesser  periods.  From 
twelve  to  fifteen  of  the  latter  are  usually  assumed.  (Cf. 
Tables  XII.  and  XIII.,  pp.    11,  12.)      The  relative  thick- 


GEOLOGICAL  TIME.  9 

ness  of  the  various  groups  of  strata  affords  the  means  of 
approximately  estimating-  the  relative  length  of  these  various 
divisions  of  time.  Of  course  we  cannot  say,  "  In  a  hun- 
dred years  on  the  average  a  stratum  of  a  certain  thick- 
ness (say  two  inches)  is  deposited,  and  therefore  a  rock- 
stratum  of  a  thousand  feet  in  thickness  is  600,000 
years  old."  For  different  rock-formations  of  equal  thick- 
ness may  have  occupied  periods  of  very  various  length 
in  their  deposition  and  consolidation.  From  the  thickness 
of  the  formation  we  may,  however,  approximately  judge  of 
the  relative  length  of  the  period  during  which  it  was 
formed. 

Of  the  four  or  five  main  periods  of  the  earth's  organic 
history,  our  acquaintance  with  which  is  indispensable  for 
our  Phylogeny  of  the  human  race,  the  first  and  oldest  is 
known  as  the  Primordial,  Archizoic,  or  Archilithic  Epoch. 
If  we  estimate  the  total  thickness  of  all  the  sedimentary 
strata  as  averaging  about  130,000  feet,  then  70,000  feet  belong 
to  this  first  epoch — more  than  one  half.  From  this  and  other 
circumstances  we  may  conclude  that  the  corresponding 
Primordial  or  Archilithic  Epoch  must  alone  have  been  con- 
siderably longer  than  the  whole  long  period  between  the 
close  of  the  Archilithic  and  the  present  time.  Probably  the 
Primordial  Epoch  was  much  longer  than  might  appear  from 
the  ratio  of  7  :  6,  which  we  have  given.  This  Epoch  is  divided 
into  three  sub-periods,  known  as  the  Laurentian,  Cambrian, 
and  Silurian,  corresponding  to  the  three  principal  groups  of 
sedimentary  rock-strata  which  constitute  the  Archilithic 
rocks.  The  enormous  length  of  time  required  for  the  forma- 
tion at  the  bottom  of  the  primordial  sea  of  these  gigantic 
strata,  of  over  70,000  feet  in  thickness,  must,  at  all  events, 


IO  THE   EVOLUTION    OF   MAN. 

have  been  many  millions  of  years.  During  that  time  there 
came  into  existence  by  spontaneous  generation  the  oldest 
and  simplest  organisms — those  in  which  life  began  upon  our 
planet — viz.,  the  Monera.  From  these,  one-celled  plants  and 
animals  first  developed — the  Amoebae  and  many  kinds  of 
Protista.  During  this  same  Archilithic  Epoch,  also,  all  the 
invertebrate  ancestors  of  the  human  race  developed  from 
these  one-celled  organisms.  We  draw  this  conclusion  from 
the  fact  that  towards  the  close  of  the  Silurian  period 
a  few  remains  of  fossil  Fishes  are  already  to  be  found,  viz., 
Selachians  and  Ganoids.  These  are,  however,  much  more 
highly  organized  and  of  later  origin  than  the  lowest 
Vertebrates  (the  Amphioxus),  or  than  the  various  skull-less 
Vertebrates  allied  to  Amphioxus,  which  must  have  lived 
during  this  time.  The  latter  must  necessarily  have  been 
preceded  by  all  the  invertebrate  ancestors  of  man.  Hence 
we  may  characterize  this  entire  epoch  as  the  "  age  of  man's 
invertebrate  ancestors ; "  or,  with  special  reference  to  the 
oldest  representatives  of  the  Vertebrate  tribe,  as  the  "  age 
of  Skull-less  Animals."  During  the  whole  Archilithic  Epoch 
the  inhabitants  of  our  planet  consisted  exclusively  of 
aquatic  forms  ;  at  least,  no  remains  of  terrestrial  animals 
or  plants  dating  from  this  period  have  as  yet  been  found. 
A  few  remains  of  land-dwelling  organisms  which  are  some- 
times referred  to  the  Silurian  Period,  are  Devonian. 

The  Primordial  Epoch  was  followed  by  the  Palaeolithic, 
Palaeozoic,  or  Primary  Epoch,  which  is  also  separable  into 
three  sub-periods :  the  Devonian,  the  Carboniferous,  and  the 
Permian.  During  the  Devonian  Period  the  Old  Eed  Sand- 
stone, or  Devonian  system  was  formed ;  during  the  Car- 
boniferous, those  great  beds  of  coal  were  deposited  which 


(  II  ) 


TABLE    XII. 

Systematic  Survey  of  the  Palaeontological  Periods,  or  the  Greater  Divisions 
in  the  llistory  of  the  Organic  Earth. 

I.  First  Epoch  :  The  Archilithic,  or  Primordial  Epoch. 
(Age  of  Skull-less  Animals  and  Seaweed  Forests.) 

1.  The  Older  Archilithic  Epoch  or  Laurentian  Period. 

2.  The  Middle  Archilithic  Epoch  „  Cambrian  Period. 

3.  The  Later  Archilithic  Epoch  „  Silurian  Period. 

II.  Second  Epoch  :  The  Palaeolithic,  or  Primary  Epoch. 

(Age  of  Fishes  and  Fern  Forests.) 

4.  The  Older  Palaeolithic  Epoch  or  Devonian  Period. 

5.  The  Middle  Palaeolithic  Epoch  „  Coal  Period. 

G.  The  Later  Palaeolithic  Epoch  „  Permian  Period. 

III.  Third  Epoch  :  The  Mesolithic,  or  Secondary  Epoch. 
(Age  of  Reptiles  and  Pine  Forests,  Conifcnr.) 

7.  The  Older  Mesolithic  Epoch  or  Triassic  Period. 

8.  The  Middle  Mesolithic  Epoch  „  Jurassic  Period. 

9.  The  Later  Mesolithic  Epoch  „  Chalk  Period. 

IV.  Fourth  Epoch  :  The  Caenolithic,  or  Tertiary  Epoch. 

(Age  of  Mammals  and  Leaf  Forests.) 

10.  The  Older  Caenolithic  Epoch  or  Eocene  Period. 

11.  The  Middle  Caenolithic  Epoch  „  Miocene  Period. 

12.  The  Later  Ca:nolithic  Epoch  „  Fliocene  Period. 

V.  Fifth  Epoch :  The  Anthropolithic,  or  Quaternary  Epoch. 
(Age  of  Man  and  Cultivated  Forests.) 

13.  The  Older  Anthropolithic  Epoch  or  Ice  Age,  Glacial  Period. 
11.  The  Middle  Anthropolithic  Epoch          „  Post  Glacial  Period. 
15.  The  Later  Anthropolithic  Epoch            „  Period  of  Culture. 

(The  Period  of  Culture  is  the  Uistoric  Period,  or  Period  of  Tradition.) 


(       12      ) 


TABLE     XIII. 

Systematic  Survey  of  the  Palteontological  Formations,  or  the  Fossiliferous 
Strata  of  the  Earth's  Crust. 


V.  Quaternary  / 

Group,         i      XIV.  Recent 
or  J         (Alluvium) 

Anthropolithic  J  XIII.  Pleistocene 
(Anthropozoic)  [        (Diluvium) 
groups  of  strata  \ 


IV.   Tertiary 

Group, 

or 

Caenolithic 

(Caenozoic) 

groups  of  strata 


III.  Secondary 

Group, 

or 

Mesolithic 

(Mesozoic) 

groups  of  strataf 


XII.  Pliocene 
(New  tertiary) 
XI.  Miocene 
(Middle  tertiar 

X.  Eocene 
(Old  tertiary) 


;>! 


IX.  Cretaceous. 


VIII.  Jura 


VII.  Trias 


II.  Primary 

Group, 

or 

Palaeolithic 

(Palaeozoic) 

groups  of  stx-ata| 


VI.  Permian 
(New  red  sand- 
stone) 

V.  Carboniferous 
(Coal) 

IV.  Devonian 
\  (Old    red    saud- 


I.  Primordial 

Group, 

or 

Archilithic 

(Archizoic) 

groups  of  strata ' 


stone) 


III.  Silurian 


II.  Cambrian 


I.  Laurentian 


36.  Present 
35.  Recent 
34.  Post  glacial 
33.  Glacial 


32.  Arvernian 
31.  Sub  Appenine 
30.  Falunian 
29.  Limburgian 
28.  Gypsum 
27.  Nummulitic 

20.  London  clay 

25.  White  chalk 

21.  Green  sand 
23.  Neocomian 

22.  Wealden 
21.  Portlandian 
20.  Oxfordian 
19.  Bath 

18.  lias 
17.  Keuper 
1<>.  Muschelkalk 
15.  Bunter  sand 

14.  Mountain 
limestone 
(Zech  stein) 

13.  Red  sandstone 

12.  Carboniferous 
sandstone 

11.  Carboniferous 
limestone 

10.  Pilton 
9.  Ilfracombe 
8.  Linton 

7.  Ludlow 
G.  Wenlock 
5.  Llandeilo 
4.  Potsdam 
3.  Longmynd 
2.  Labrador 
1.  Ottawa 


Upper  alluvial 
Lower  alluvial 
Upper  diluvial 
Lower  diluvial 


Upper  pliocene 
Lower  pliocene 
Upper  miocene 
Lower  miocene 
Upper  eocene 
Middle  eocene 
Lower  eocene 

Upper  cretaceous 
Middle  cretaceous 
Lower  cretaceous 
The  Kentish  Weald 
Upper  oolite 
Middle  oolite 
Lower  oolite 
Lias  formation 
Upper  trias 
Middle  trias 
Lower  trias 

Upper  Permian 


Lower  Permian 
Upper  carbonifer- 
ous 
Lower  carbonifer- 
ous 
Upper  Devonian 
Middle  Devonian 
Lower  Devonian 

Upper  Silurian 
Middle  Silurian 
Lower  Silurian 
Upper  Cambrian 
Lower  Cambrian 
Upper  Laurentian 
Lower  Laurentian 


GEOLOGICAL   PERIODS.  1 3 

supply  us  with  our  principal  fuel ;  in  the  Permian,  the 
New  Red  Sandstone,  the  Magnesian  Limestone  (Zechstein), 
and  the  Cupriferous  Slate  were  formed.  The  approxi- 
mate thickness  of  this  entire  group  of  strata  is  esti- 
mated at  42,000  feet  at  most ;  some  geologists  make  it 
somewhat  more,  others  considerably  less.  In  any  case, 
this  Palaeolithic  Epoch,  taken  as  a  whole,  is  consider- 
ably shorter  than  the  Archilithic,  but  yet  is  considerably 
longer  than  all  the  following  Epochs  taken  together.  The 
strata  deposited  during  this  Primary  Epoch  supply  fossil 
animal  remains  in  great  abundance ;  besides  numerous 
species  of  Invertebrates  we  find  also  very  many  Verte- 
brates— Fishes  preponderating.  As  early  as  the  Devonian, 
and  even  during  the  Carboniferous  and  the  Permian 
Periods,  there  existed  so  great  a  number  of  Fishes,  espe- 
cially Primitive  Fishes  (Sharks)  and  Ganoids,  that  we  may 
designate  the  entire  Palaeolithic  Period  as  the  Age  of  Fishes. 
The  Palaeozoic  Ganoids  especially  are  represented  by  a 
large  number  of  forms. 

But  even  during  this  period  some  Fishes  began  to 
accustom  themselves  to  living  upon  the  land,  and  thus  gave 
rise  to  the  Amphibian  class.  Even  in  the  carboniferous 
system  we  find  fossil  remains  of  Amphibia — the  earliest 
terrestrial  and  air-breathing  animals.  In  the  Permian 
Period  the  variety  of  these  Amphibia  becomes  greater.  To- 
\\  aids  its  close  the  first  Amnion-animals,  the  tribal  ancestors 
of  the  true  higher  Vertebi-ate  classes,  seem  first  to  appear. 
These  are  a  few  lizard-like  animals,  of  which  the  Protero- 
saurus  from  the  Cupriferous  Slate  at  Eisenach  is  the  best 
known.  The  appearance  of  the  most  ancient  Amnion 
Animals  (Amniota),  to  which  the  common  parent-form  of 


14  THE   EVOLUTION    OF   MAN. 

Reptiles,  Birds,  and  Mammals  must  have  belonged,  seems 
in  fact  to  be  referred  by  these  oldest  reptilian  remains  back 
to  the  close  of  the  Palaeolithic  Epoch.  During  this  Epoch 
the  ancestors  of  the  human  race  must  accordingly  have 
been  represented,  first  by  true  Fishes,  then  by  Mud-Fishes 
{Dlpneusta)  and  Amphibia,  and  finally  by  the  oldest 
Amnion  Animals,  the  Protamnia. 

After  the  Palaeolithic  Epoch  comes  a  third  main  division 
of  the  earth's  organic  history,  known  as  the  Mesolithic,  or 
Secondary  Epoch.  This  is  again  distinguished  into  three 
subdivisions — the  Triassic,  the  Jurassic,  and  the  Cretaceous 
Periods.  The  approximate  thickness  of  the  strata-groups, 
formed  during  these  three  Periods  from  the  beginning  of 
the  Triassic  down  to  the  end  of  the  Cretaceous  Period, 
amounts  in  all  to  about  15,000  feet,  not  one  half  the  thick- 
ness of  the  Palaeolithic  deposits.  During  this  Epoch  a  very 
great  and  varied  development  took  place  in  all  divisions  of 
the  animal  kingdom.  In  the  vertebrate  tribe  especially  a 
number  of  new  and  interesting  forms  developed.  Among 
Fishes  the  Osseous  Fishes  (Teleostei)  now  first  appear.  But 
the  Reptiles  surpass  all  others  both  in  numbers  and  in 
diversity  of  species — the  most  remarkable  and  the  most 
familiar  forms  being  the  gigantic  extinct  Dragons  (Dino- 
saurians),  the  Sea-Dragons  (Halisaurians),  and  the  Flying 
Lizards  (Pterosaurians).  In  reference  to  this  predominance  of 
the  reptilian  class  this  time  is  known  as  the  age  of  reptiles. 
But  the  class  of  Birds  also  developed  during  this  period, 
undoubtedly  originated  from  a  branch  of  the  lizard-like 
Rep  tiles.  This  is  shown  by  the  similar  embryology  of  Birds 
and  of  Reptiles,  by  their  Comparative  Anatomy,  and  also  by 
the  fact  that  we  know  of  fossil  birds  with  toothed  jaws 


FAUNA  OF   THE   GEOLOGICAL   PERIODS.  I  5 

and  with  lizard's  tail,  belonging-  to  this  period  (Odon- 
tomis  Arcftceopteryx).  Finally,  it  was  during  this  period 
that  there  appeared  upon  the  scene  that  most  perfect  and, 
for  us,  most  important  vertebrate  class,  the  mammalian 
class.  The  oldest  fossil  remains  of  these  have  been  found 
in  the  most  recent  Triassic  strata,  viz.,  molar  teeth  of 
a  small  insectivorous  Pouched  Animal  (Marsupial).  Numer- 
ous remains  occur  somewhat  later  in  the  Jura  system,  and 
a  few  in  the  chalk.  All  the  remains  of  Mammals  from  this 
Mesolithic  Epoch  with  which  we  are  acquainted  belong  to 
the  low  Pouched  Animal  division ;  and  among  these  were 
undoubtedly  the  ancestors  of  Man.  On  the  other  hand, 
not  a  single  undisputed  relic  has  yet  been  discovered 
throughout  all  this  period  of  one  of  the  higher  Mammals 
(Placentalia).  This  last  division,  of  which  Man  is  a  member, 
did  not  develop  till  later,  in  the  immediately  subsequent 
Tertiary  Epoch. 

The  fourth  main  division  of  the  history  of  the  organic 
earth,  the  Tertiary,  Caenozoic,  or  Csenolithic  Epoch,  was  of 
much  shorter  duration  than  the  preceding.  For  the  strata 
deposited  during  this  period  are  in  all  only  about  3000  feet 
in  thickness.  This  Epoch,  also,  is  divided  into  three  sub- 
divisions, known  as  the  Eocene,  Miocene,  and  Pliocene 
Periods.  During  these  periods  the  most  diverse  develop- 
ment of  the  higher  classes  of  plants  and  animals  took  place 
and  the  fauna  and  flora  of  our  globe  now  approached 
nearer  and  nearer  to  their  present  character.  The  most 
highly  developed  class  of  animals,  that  of  Mammals,  now 
attained  pre-eminence.  This  Tertiary  Epoch  may,  therefore, 
be  called  the  age  of  Mammals.  The  most  perfect  section 
of  this  class,  the  Placental  Animals,  among  which  is  Man, 


1 6  THE    EVOLUTION   OF   MAN. 

now  first  appeared.  The  first  appearance  of  Man — or  to 
speak  more  correctly — the  development  of  man  from  the 
most  nearly  allied  ape-form,  dates  probably  either  from  the 
Miocene  or  the  Pliocene  Period, — from  the  middle  or  the 
latest  section  of  the  Tertiary  Epoch.  Perhaps,  as  is  assumed 
by  others,  Man  strictly  so-called,  i.e.,  Man  gifted  with 
language,  first  developed  from  the  speechless  man-like  Apes, 
in  the  subsequent  Anthropolithic  Age. 

At  all  events,  the  perfect  development  and  distribution 
of  the  various  races  of  Man  dates  from  the  fifth  and  last 
main  division  of  the  organic  history  of  the  earth,  and  hence 
this  Epoch  has  been  called  the  Anthropolithic,  or  Anthro- 
pozoic,  and  also  the  Quaternary  Epoch.  It  is  true  that,  in 
the  present  imperfect  state  of  our  palseontological  and 
prehistoric  knowledge,  we  cannot  solve  the  problem  as  to 
whether  the  development  of  Man  from  the  nearest  allied 
Ape-forms  took  place  in  the  beginning  of  this  Anthropolithic 
Epoch,  or  as  early  as  the  middle  or  towards  the  close  of  the 
preceding  Tertiary  Epoch.  This  much,  however,  is  certain, 
that  the  true  development  of  human  culture  dates  only 
from  the  Anthropolithic  Epoch,  and  that  this  latter  con- 
stitutes only  an  insignificantly  small  section  of  the  entire 
enormous  period  of  time  occupied  in  the  development  of 
the  organic  earth.  When  we  reflect  upon  this,  it  appears 
absurd  to  speak  of  the  brief  span  of  man's  period  of  cul- 
ture as  "  the  world's  history."  This  so-called  History  of 
the  World  does  not  amount  approximately  to  even  one- 
half  per  cent,  of  the  length  of  those  enormous  periods 
which  have  passed  away  from  the  beginning  of  the  earth's 
organic  history  down  to  the  present  time.     For  this  World's 


THE   "  AGE   OF   MAN."  1 7 

History,  or  more  correctly,  History  of  People,  is  itself 
only  the  latter  half  of  the  Anthropolithic  Epoch,  while 
even  the  first  half  of  this  Epoch  must  be  reckoned  as  a 
prehistoric  period.  Hence  this  last  main  period,  reaching 
from  the  close  of  the  Granolithic  Epoch  to  the  present  time, 
can  only  be  called  the  "  age  of  man,"  inasmuch  as  the 
diffusion  and  differentiation  of  the  different  species  and 
races  of  man,  which  have  so  powerfully  influenced  all  the 
rest  of  the  organic  population  of  the  globe,  took  place 
during  its  course. 

Since  the  awakening  of  the  human  consciousness, 
human  vanity  and  human  arrogance  have  delighted  in 
regarding  Man  as  the  real  main-purpose  and  end  of  all 
earthly  life,  and  as  the  centre  of  terrestrial  Nature,  for  whose 
use  and  service  all  the  activities  of  the  rest  of  creation  were 
from  the  first  defined  or  predestined  by  a  "wise  providence." 
How  utterly  baseless  these  presumptuous  anthropocentric 
conceptions  are,  nothing  could  evince  more  strikingly  than 
a  comparison  of  the  duration  of  the  Anthropozoic  or  Quater- 
nary Epoch  with  that  of  the  preceding  Epochs.  For  even 
though  the  Anthropolithic  Epoch  may  embrace  several  hun- 
dreds of  thousands  of  years,  how  small  is  this  time  when 
compared  with  the  millions  of  years  that  have  elapsed  since 
the  beginning  of  the  world's  organic  history  down  to  the 
first  appearance  of  the  human  race  ! 

If  the  entire  duration  of  the  organic  history  of  the  earth, 
from  the  generation  of  the  first  Monera  down  to  the  present 
day,  is  divided  into  a  hundred  equal  parts,  and  if  then, 
corresponding  with  the  relative  average  thickness  of  the 
intervening   strata-systems,  the  respective  percentages  are 


1 8  THE   EVOLUTION   OF   MAN. 

assigned  to  the  relative  durations  of  the  five  main  divisions 
or  Epochs,  the  latter  will  be  found  to  be  about  as  follows  : — 

I.  Archilithic,  or  archizoic  (primordial)  Epoch         .         .     53.6 

II.  Palaeolithic,  or  palaeozoic  (primary)  Epoch  .         .     32.1 

III.  Mesolithic,  or  mesozoic  (secondary)  Epoch  .         .11.5 

IV.  CiBriolithic,  or  cenozoic  (tertiary)  Epoch      .  .         .       2.3 
V.  Anthropolithic,  or  anthropozoic  (quaternary)  Epoch  .       0.5 

Total     ...     100.0 

The  relative  durations  of  the  five  main  epochs  of  the 
earth's  organic  history,  are  yet  more  clearly  seen  in  the 
opposite  Table  (XIV.),  in  which  the  relative  thicknesses  of 
the  strata  systems  deposited  within  these  Epochs  is  repre- 
sented on  a  scale  corresponding  tto  their  actual  depths. 

This  table  shows  that  the  period  of  the  so-called  History 
of  the  World  forms  but  an  inconsiderable  span  in  comparison 
with  the  immeasurable  duration  of  those  earlier  epochs  during 
which  Man  did  not  exist  upon  this  planet.  Even  the  great 
Csenozoic  Epoch,  the  so-called  Tertiary  Epoch,  during  which 
the  Placental  Animals,  the  higher  Mammals,  developed, 
includes  but  little  more  than  two  per  cent,  of  the  whole 
enormous  duration  of  the  organic  history  of  the  world.128 

And  now  before  we  turn  to  our  proper  phylogenetic 
task ;  before,  guided  by  our  knowledge  of  ontogenetic  facts 
and  by  the  fundamental  law  of  Biogeny,  we  attempt  to 
trace  step  by  step  the  history  of  the  palseontological  evo- 
lution of  our  animal  ancestors,  let  us  turn  aside  for  a  short 
time  into  another  and  apparently  very  different  and  very 
remote  department  of  science,  a  general  review  of  which 
will  make  the  solution  of  the  difficult  problems  which 
now  rise  before  us  very  much  easier.     The  science  is  that 


(     19    ) 


TABLE  XIV. 

Systematic  Survey  of  the  Neptunian  fossiliferous  strata  of  the  earth  with 
reference  to  their  relative  sectional  thickness  (130,000  feet  circa). 


IV.      Ca?nolithic  Strata, 
circa  3000  feet. 

Pliocene,  Miocene,  Eocene. 

III.     Mesolithic  Strata. 

IX.     Chalk  System. 

Deposits  of  the 
Secondary  Epoch,  circa 

VIII.     Jurassic  System. 

15,000  feet. 

VII.     Triassic  System 

II.     Palaeolithic  Strata. 

VI.     Permian  System. 

Deposits  of  the 
Primary  Epoch,  circa 

V.     Coal  System. 

42,000  feet. 

IV.     Devonian  System. 

I.     Archilithic  Strata. 

III.     Silurian  System,  circa 
22,000  feet. 

Deposits  of  the 
Primordial  Epoch,  circs, 

II.     Cambrian  System,  circa 
18,000  feet. 

70,000  feet. 

I.     Laurentian  System,  circa 
30,000  feet. 

20  THE   EVOLUTION   OF   MAN. 

of  Comparative  Philology.  Ever  since  Darwin,  by  the  theory 
of  Natural  Selection,  infused  new  life  into  Biology,  and  raised 
the  fundamental  question  of  development  in  every  branch 
of  science,  attention  has  frequently  and  from  very  different 
quarters  been  called  to  the  remarkable  parallelism,  which 
exists  between  the  evolution  of  the  various  human  languages 
and  the  evolution  of  organic  species.  The  comparison  is 
quite  justifiable  and  very  instructive.  Indeed  it  is  hardly 
possible  to  find  an  analogy  better  adapted  to  throw  a  clear 
light  on  many  obscure  and  difficult  facts  in  the  evolution  of 
species,  which  is  governed  and  directed  by  the  same  natural 
laws  which  guide  the  course  of  the  evolution  of  language. 

All  philologists  who  have  made  any  progress  in  their 
science,  now  unanimously  agree  that  all  human  languages 
have  developed  slowly  and  by  degrees  from  the  simplest 
rudiments.  On  the  other  hand,  the  strange  proposition 
which  till  thirty  years  ago  was  defended  by  eminent  au- 
thorities, that  language  is  a  divine  gift,  is  now  universally 
rejected,  or  at  best  defended  only  by  theologians  and  by 
people  who  have  no  conception  of  natural  evolution.  Such 
brilliant  results  have  been  attained  in  Comparative  Philology 
that  only  one  who  is  wilfully  blind  can  fail  to  recognize  the 
natural  evolution  of  language.  The  latter  is  necessarily 
evident  to  the  student  of  nature.  For  speech  is  a  physio- 
logical function  of  the  human  organism,  developing  simul- 
taneously with  its  special  organs,  the  larynx  and  the  tongue, 
and  simultaneously  with  the  functions  of  the  brain.  It  is, 
therefore,  quite  natural  that  in  the  history  of  the  evolution 
of  languages,  and  in  their  whole  system,  we  should  find  the 
same  correlations  as  in  the  history  of  the  evolution  of 
organic  species  and  in   their  whole   system.     The  various 


METHOD   OF    COMPARATIVE   PHILOLOGY.  21 

larger  and  smaller  groups  of  speech-fprms,  which  are  distin- 
guished in  Comparative  Philology  as  primitive  languages, 
fundamental  languages,  parent  languages,  derived  languages, 
dialects,  patois,  etc.,  correspond  perfectly  in  their  mode  of 
development  with  the  various  larger  and  smaller  groups  of 
organisms  classed  in  systems  of  Zoology  and  Botany  as 
tribes,  classes,  orders,  families,  genera,  species,  and  varie- 
ties of  the  animal  and  vegetable  kingdoms.  The  relations 
between  these  various  systematic  groups,  or  categories,  are 
in  both  cases  identical;  moreover,  evolution  follows  the 
same  course  in  one  case  as  in  the  other.  This  instructive 
comparison  was  first  elaborated  by  one  of  the  most  eminent 
of  German  philologists,  one  who,  unfortunately,  died  pre- 
maturely— August  Schleicher,  not  only  a  philologist  but  also 
a  learned  botanist.  In  his  more  important  works,  the  Com- 
parative Anatomy  and  evolutionary  history  of  languages  is 
treated  by  the  same  phylogenetic  method  which  we  employ 
in  the  Comparative  Anatomy  and  evolutionary  history  of 
animal  forms.  He  has  especially  applied  this  method  to 
the  Indo-Germanic  family  of  languages  ;  and  in  his  little 
treatise  on  "  The  Darwinian  Theory  and  the  Science  of 
Language "  ("  Die  Darwin'sche  Theorie  und  die  Sprach- 
wissenschaft "),  he  illustrated  it  by  means  of  a  synoptical 
pedigree  of  the  Indo-Germanic  family  of  languages.129 

If  the  formation  of  the  various  branch  languages  which 
have  developed  from  the  common  root  of  the  primitive 
Indo-Germanic  tongue  is  studied  with  the  aid  of  this  pedi- 
gree, a  very  clear  idea  of  their  Phylogeny  will  be  acquired. 
At  the  same  time  it  becomes  evident  how  entirely  analogous 
is  the  evolution  of  the  greater  and  lesser  groups  of  the 
Vertebrates,  which  have  sprung  from  the  one  common  root- 


22  THE   EVOLUTION   OF   MAN. 

form  of  the  primitive  Vertebrates.  The  primitive  lndo- 
Germanic  root-tongue  first  separated  into  two  chief  stems  : 
the  Slavo-Germanic  and  the  Ario-Romanic  main-trunks. 
The  Slavo-Germanic  then  branched  into  a  primitive  German 
and  a  primitive  Slavo-Lettic  tongue.  Similarly,  the  Ario- 
Romanic  split  up  into  a  primitive  Arian  and  a  primitive 
Grseco-Romanic  language  (p.  23).  If  we  continue  our 
examination  of  this  pedigree  of  the  four  primitive  Indo- 
Germanic  languages,  we  find  that  the  primitive  Germanic 
tongue  divided  into  three  chief  branches — a  Scandinavian, 
a  Gothic,  and  a  Teutonic  branch.  From  the  Teutonic  branch 
proceeded,  on  the  one  hand,  High  German,  and,  on  the 
other  hand,  Low  German,  to  which  latter  belong  the  various 
Friesian,  Saxon,  and  Low  German  dialects.  Similarly,  the 
Slavo-Lettic  tongue  developed  first  into  a  Baltic  and  a 
Slavonic  language.  From  the  Baltic  spring  the  Lettic, 
Lithuanian,  and  Old  Prussian  dialects.  The  Slavic,  on  the 
other  hand,  give  rise,  in  the  South-east,  to  the  Russian  and 
the  South  Slavic  dialects,  and,  in  the  West,  to  the  Polish 
and  Czech  dialects. 

Turning  now  to  the  other  main  stem  of  the  Indo- 
Germanic  languages  and  its  branches — the  primitive  Ario- 
Romanic — it  is  found  to  develop  with  the  same  luxuriance. 
The  primitive  Grseco-Romanic  language  gave  rise,  on  the 
one  hand,  to  the  Thracian  language  (Albanian  Greek),  and 
on  the  other,  to  the  Italo- Keltic.  From  the  latter  in  turn 
sprung  two  divergent  branches — in  the  South,  the  Italian 
branch  (Romanic  and  Latin),  and  in  the  North,  the  Keltic, 
from  which  arose  all  the  different  British  (Old  British,  Old 
Scottish,  and  Irish"1  and  Gallic  tongues.  The  numerous 
Iranian  and  Indian  dialects  branched  out  in  the  same  way 
from  the  primitive  Arian  language. 


(     23     ) 
TABLE    XV. 

Pedigree  of    the  Indo-Germanic  Languages. 


Anglo  Saxons  High  Germans 

Lithuanians     Ancient  Prussians  Low  Germans 

Letts  Netherlander 


Ealtic  Races 


Ancient  Saxons 


Serbians 
Polish 
Czechs     I 


Saxons 


Friesians 


West  Sclaves 

Russians 
South  Sclaves 


South-east  Sclaves 


Sclaves 


Low  Germans 


Scandinavians 


Goths 


Germans 


Primitive  Germans 


Sclavo-Letts 


Romans 


Ancient  British 
Ancient  Scotch 
Irish 


Latins  ^TT" 
i        Gaels 


Gauls 


Italians 


Brittanese 
Kelts 


Sclavo  Germans 


Italo  Kelts 


Albanese 


Greeks 


Primitive  Thracians 
Indians     Iranians 


Arians 


Graeco-Romans 


Ario-Romans 


Indc-Germans 


24  THE    EVOLUTION   OF   MAN. 

A  close  study  of  this  pedigree  of  the  Indo-Germanic 
languages  is,  in  many  respects,  of  great  interest.  Com- 
parative Philology,  to  which  we  are  indebted  for  our  know- 
ledge of  this  subject,  thus  shows  itself  to  be  a  true  science — 
a  natiual  science.  It,  indeed,  long  ago  anticipated  in  its 
own  province  the  ph}dogenetic  method  with  the  aid  of 
which  we  now  attain  the  highest  results  in  Zoology  and 
and  in  Botany.  And  here  I  cannot  refrain  from  remarking 
how  much  to  the  advantage  of  our  general  culture  it  would 
be  if  the  study  of  languages  (which  is  undoubtedly  one  of 
the  most  powei'ful  means  of  culture)  were  comparatively 
prosecuted;  and  if  our  cut  and  dried  Philology  were  re- 
placed by  a  living,  many-sided,  comparative  study  of  lan- 
guages. The  latter  stands  in  the  same  relation  to  the 
former  as  the  living  history  of  organic  evolution  does  to 
the  lifeless  classification  of  species.  How  much  deeper 
would  the  interest  taken  in  the  study  of  language  by  the 
students  in  our  schools  be,  and  how  much  more  vivid  would 
be  the  results  if  even  the  first  elements  of  Comparative 
Philology  were  taught  instead  of  the  distasteful  composi- 
tion of  Latin  exercises  in  Ciceronian  style  ! 

I  have  entered  with  this  detail  into  the  "  Comparative 
Anatomy  "  and  the  history  of  the  evolution  of  languages, 
because  it  is  unsurpassed  as  a  means  of  illustrating  the 
Phylogeny  of  organic  species.  We  find  that  in  structure 
and  in  development  these  primitive  languages,  parent 
languages,  derived  languages,  and  dialects,  correspond 
exactly  like  the  classes,  orders,  genera,  and  species  of  the 
animal  kingdom.  The  "  natural  system  "  is  in  both  cases 
phylogenetic.  Just  as  Comparative  Anatomy,  Ontogeny,  and 
Palaeontology  afford   certain    proof    that    all    Vertebrates, 


*  MAN   DESCENDED  FROM  EXTINCT    FORMS.  25 

whether  extinct  or  extant,  are  descended  from  a  common 
ancestral  form,  so  does  the  comparative  study  of  the  dead 
and  living  Indo-Germanic  language  absolutely  convince 
us  that  all  these  languages  have  sprung  from  a  common 
origin.  This  monophyletic  view  is  unanimously  adopted  by 
all  linguists  of  importance  who  have  studied  the  question, 
and  who  are  capable  of  passing  a  critical  judgment  upon  it.130 
The  point,  however,  to  which  I  would  specially  call  your 
attention  in  this  comparison  between  the  various  branches, 
on  the  one  hand,  of  the  Indo-Germanic  language,  and,  on  the 
other,  of  the  vertebrate  tribe,  is  that  the  direct  descendants 
must  never  be  confounded  with  the  collateral  lines,  nor  the 
extinct  with  the  extant  forms.  This  mistake  is  often 
made,  and  results  in  the  formation  of  erroneous  notions  of 
which  our  opponents  often  take  advantage  in  order  to 
oppose  the  whole  theory  of  descent.  When,  for  instance,  it 
is  said  that  human  beings  are  descended  from  Apes,  the 
latter  from  Semi-apes,  and  the  Semi-apes  from  Pouched 
Animals  (Marsupialia),  very  many  people  think  only  of  the 
familiar  living  species  of  these  different  mammalian  orders, 
such  as  are  to  be  found  stuffed  in  our  museums.  Now,  our 
opponents  attribute  this  erroneous  view  to  us,  and,  with 
more  craft  than  judgment,  declare  the  thing  impossible  ;  or 
else  they  ask  us  as  a  physiological  experiment  to  transform 
a  Kangaroo  into  a  Semi-ape,  this  into  a  Gorilla,  and  the 
Gorilla  into  a  Man.  Their  demand  is  as  childish  as  the 
conception  on  which  it  is  founded  is  erroneous;  for  all 
these  extant  forms  have  varied  more  or  less  from  their 
common  parent-form,  and  none  of  them  are  capable  of  pro- 
ducing the  same  divergent  posterity  which  were  really 
produced  thousands  of  years  ago  by  that  parent-form.131 


26  THE   EVOLUTION    OF   MAN. 

There  is  no  doubt  that  Man  is  descended  from  an  extinct 
mammalian  form,  which,  if  we  could  see  it,  we  should 
certainly  class  with  the  Apes.  It  is  equally  certain  that 
this  primitive  Ape  in  turn  descended  from  an  imknown 
Semi-ape,  and  the  latter  from  an  extinct  Pouched  Animal. 
But  then  it  is  beyond  a  doubt  that  it  is  only  in  respect  of 
essential  internal  structure,  and  on  account  of  their  similarity 
in  the  distinctive  anatomical  characters  of  the  order,  that  all 
these  extinct  ancestral  forms  can  be  spoken  of  as  members 
of  the  yet  extant  mammalian  orders.  In  external  form,  in 
generic  and  specific  characters,  they  must  have  been  more  or 
less — perhaps  even  greatly — different  from  all  living  repre- 
sentatives of  the  orders  to  which  they  belonged.  For  it 
must  be  accepted  as  a  quite  universal  and  natural  fact  in 
phylogenetic  evolution  that  the  parent-forms  themselves, 
with  their  specific  characters,  became  extinct  at  a  more  or 
less  distant  period.  Those  extant  forms  which  come  nearest 
to  them,  yet  differ  from  them  more  or  less,  perhaps  even 
very  essentially.  Hence  in  our  phylogenetic  researches 
and  in  our  comparative  view  of  the  still  living  divergent 
descendants  all  we  can  undertake  to  do  is  to  determine 
how  far  the  latter  depart  from  the  parent-form.  We  may 
quite  confidently  assume  that  no  single  older  parent-form 
has  reproduced  itself  without  modification  down  to  our  time. 

We  find  this  same  state  of  things  on  comparing  various 
extinct  and  living  languages,  which  have  sprung  from  one 
common  primitive  tongue.  If,  from  this  point  of  view,  we 
examine  the  genealogical  tree  of  the  Indo-Germanic 
languages,  we  may  conclude,  on  a  priori  grounds,  that  all 
the  earlier  primitive  languages,  fundamental  languages,  and 
ancestral    languages,   from    which   the   living   dialects   are 


COMPARATIVE    METHODS   OF    PHILOLOGY  AND   ZOOLOGY.    2? 

descended  in  the  first  or  second  degree,  have  been  extinct 
for  a  longer  or  shorter  period.  And  this  is  the  case.  The 
Ario-Romanic  and  the  Sclavo-Germanic  tongues  have  long 
been  altogether  extinct,  as  are  also  the  primitive  Arian  and 
Grreco-Romanic,  the  Sclavo-Lettic,  and  primitive  Germanic 
languages.  Some  even  of  the  languages  descended  from 
these  have  also  long  been  dead,  and  all  those  of  the  Indo- 
Germanic  branch  which  are  yet  extant,  are  akin  only  in 
so  far  as  they  are  divergent  descendants  of  common  parent- 
forms.  Some  have  diverged  from  this  ancestral  form  more, 
others  less. 

This  easily  demonstrable  fact  very  well  illustrates 
analogous  facts  in  the  descent  of  vertebrate  species.  Phy- 
logenetic  "  Comparative  Philology,"  as  a  powerful  ally,  sup- 
ports phylogenetic  "  Comparative  Zoology."  The  former  can, 
however,  adduce  far  more  direct  evidence  than  the  latter, 
because  the  palreontological  materials  of  Philology,  the 
ancient  monuments  of  extinct  tongues,  have  been  far  better 
preserved  than  the  paloBontological  materials  of  Comparative 
Zoology,  the  fossil  bones  of  vertebrates.  The  more  these 
analogous  conditions  are  considered,  the  more  convincing 
is  their  force. 

We  shall  presently  find  that  we  can  trace  back  the 
genealogical  line  of  Man,  not  only  to  the  lower  Mammals, 
but  even  to  the  Amphibia,  to  the  shark -like  Primitive  Fishes, 
and  even  far  below  these,  to  the  skull-less  Vertebrates  allied 
to  the  Amphioxus.  It  must  be  remembered  this  does  not 
mean  that  the  living  Amphioxus,  Shark,  or  Amphibian  accu- 
rately represent  the  outward  appearance  of  the  parent-forms 
of  which  we  speak.  Still  less  does  it  mean  that  the 
Amphioxus,  or  the  Shark  of  our  day,  or  any  extant  species 


28  THE  EVOLUTION   OF  MAN. 

of  Amphibian  is  an  actual  parent-form  of  the  higher  Ver- 
tebrates and  of  Man.  On  the  contrary,  this  important 
assertion  must  be  clearly  understood  to  mean,  that  the  living 
forms,  which  have  been  mentioned,  are  side  branches,  which 
are  much  more  nearly  allied,  and  similar  to  the  extinct 
common  parent-forms,  than  any  other  known  animal  forms. 
In  their  internal  characteristic  structure  they  remain  so 
similar  to  the  unknown  parent-forms,  that  we  should  class 
them  both  in  one  order,  if  we  had  the  latter  before  us  in 
a  living  state.  But  the  direct  descendants  of  the  primitive 
forms  have  never  remained  unmodified.  Hence  it  is 
quite  impossible  that  among  the  living  species  of  animals 
we  should  find  the  actual  ancestors  of  the  human  race  in 
their  characteristic  specific  forms.  The  essential  and  charac- 
teristic features,  which  more  or  less  closely  connect  living- 
forms  with  the  extinct  common  parent-forms,  are  to  be 
found  in  the  internal  structure  of  the  body,  not  in  the 
external  specific  form.  The  latter  has  been  much  modified 
by  adaptation.  The  former  has  been  more  or  less  retained 
by  heredity. 

Comparative  Anatomy  and  Ontogeny  indisputably  prove 
that  Man  is  a  true  Vertebrate,  so  that  the  special  genealo- 
gical line  of  Man  must  of  course  be  connected  with  that  of 
all  those  Vertebrates  which  are  descended  from  the  same 
common  root.  Moreover,  on  many  definite  grounds,  sup- 
plied by  Comparative  Anatomy  and  Ontogeny,  we  must 
assume  only  one  common  origin  for  all  Vertebrates — 
a  monophyletic  descent.  Indeed,  if  the  theory  of  descent 
is  correct,  all  Vertebrates,  Man  included,  can  only  have 
descended  from  a  single  common  parent-form — from  a  single 
primitive  Vertebrate  species.  The  genealogical  line  of  the 
Vertebrates,  therefore,  is  also  that  of  Man. 


AMCEBOID  ANCESTORS.  29 

Our  task  of  ascertaining  a  pedigree  of  Man  thus  widens 
into  the  more  considerable  task  of  constructing  the  pedigree 
of  all  the  Vertebrates.  This  is  connected,  as  we  learned  from 
the  Comparative  Anatomy  and  Ontogenjr  of  the  Amphioxus 
and  of  the  Ascidian,  with  the  pedigree  of  the  Invertebrate 
animals,  and  directly  Avith  that  of  the  Worms,  while  no  con- 
nection can  be  shown  with  the  genealogy  of  the  indepen- 
dent tribes  of  the  Articulated  Animals  (Arthropoda),  Soft- 
bodied  Animals  (Mollusca),  and  Star-animals  (Echinoderma). 
As  the  Ascidian  belongs  to  the  Mantled  Animals  (Tunicata), 
and  as  this  class  can  only  be  referred  to  the  great  Worm 
tribe,  we  must,  aided  by  Comparative  Anatomy  and  Onto- 
geny, further  trace  our  pedigree  down  through  various  stages 
to  the  lowest  forms  of  Worms.  This  necessarily  brings  us 
to  the  Gastnea,  that  most  important  animal  form  in  which 
we  recognize  the  simplest  conceivable  prototype  of  an  animal 
with  two  germ -layers.  The  Gastrrea  itself  must  have  ori- 
ginated from  among  those  lowest  of  all  simple  animal  forms, 
which  are  now  included  by  the  name  of  Primitive  Animals 
(Protozoa).  Among  these  we  have  already  considered  that 
primitive  form  which  possesses  most  interest  for  us — the 
one-celled  Amoeba,  the  peculiar  significance. of  which  depends 
on  its  resemblance  to  the  human  egg-cell.  Here  we  have 
reached  the  lowest  of  those  impregnable  points,  at  which 
the  value  of  our  fundamental  law  of  Biogeny  is  directly 
found,  and  at  which,  from  the  embryonic  evolutionary  stage, 
we  can  directly  infer  the  extinct  parent-form.  The  amoeboid 
nature  of  the  young  egg-cell,  and  the  one-celled  condition 
in  which  each  Man  begins  his  existence  as  a  simple  parent- 
cell  or  cy tula-cell,  justify  us  in  affirming  that  the  oldest 
ancestors  of  the  human  race  (as  of  the  whole  animal 
kingdom)  were  simple  amoeboid  cells. 


30  THE    EVOLUTION   OF   MAN. 

Here  arises  another  question  :  "  Whence,  in  the  begin- 
ning of  the  organic  history  of  the  earth,  at  the  commence- 
ment of  the  Laurentian  period,  came  the  earliest  Amoebae  ?  " 
To  this  there  is  but  one  reply.  Like  all  one-celled  organ- 
isms, the  Amoebae  have  originally  developed  only  from  the 
simplest  organisms  know  to  us,  the  Monera.  These  Monera, 
which  we  have  already  described,  are  also  the  simplest  con- 
ceivable organisms.  Their  body  has  no  definite  form,  and 
is  but  a  particle  of  primitive  slime  (plasson) — a  little  mass 
of  living  albumen,  performing  all  the  essential  functions  of 
life,  and  everywhere  met  with  as  the  material  basis  of  life. 
This  brings  us  to  the  last,  or  perhaps  the  first  question  in 
the  history  of  evolution— the  question  as  to  the  origin  of 
the  Monera.  And  this  is  the  momentous  question  as  to  the 
prime  origin  of  life — the  question  of  spontaneous  generation 
(generatio  spontanea  or  cequivoca). 

We  have  neither  time,  nor  indeed  have  we  any  occasion, 
to  discuss  at  length  the  weighty  question  of  spontaneous 
generation.  On  this  subject  I  must  refer  you  to  my 
"  History  of  Creation,"  and,  especially,  to  the  second  book 
of  the  Generelle  Morphologic,  and  to  the  discussion  on 
Monera  and  spontaneous  generation  in  my  "  Studien  liber 
Moneren  und  andere  Protista." 132  I  have  there  stated 
my  own  views  on  this  important  subject  in  very  great 
detail.  Here  I  will  only  say  a  few  words  on  the  ob- 
scure question  as  to  the  first  origin  of  life,  and  will  answer 
it  so  far  as  it  concerns  our  radical  conception  of  the 
history  of  organic  evolution.  In  the  definite,  limited 
sense  in  which  I  maintain  spontaneous  generation  {gene- 
ratio  spontanea)  and  assume  it  as  a  necessary  hypo- 
thesis in  explanation  of  the  first  beginning  of  life  upon 


SPONTANEOUS    GENERATION.  3 1 

the  earth,  it  merely  implies  the  origin  of  Monera  from 
inorganic  carbon  compounds.  When  animated  bodies  first 
appeared  on  our  planet,  previously  without  life,  there  must, 
in  the  first  place,  have  been  formed,  by  a  process  purely 
chemical,  from  purely  inorganic  carbon  combinations,  that 
very  complex  nitrogenized  carbon  compound  which  we  call 
plasson,  or  "  primitive  slime,"  and  which  is  the  oldest  material 
substance  in  which  all  vital  activities  are  embodied.  In 
the  lowest  depths  of  the  sea  such  homogeneous  amorphous 
protoplasm  probably  still  lives,  in  its  simplest  character,  under 
the  name  of  Bathybius.137  Each  individual  living  particle 
of  this  structureless  mass  is  called  a  Moneron.  The  oldest 
Monera  originated  in  the  sea  by  spontaneous  generation, 
just  as  crystals  form  in  the  matrix.  This  assumption  is 
required  by  the  demand  of  the  human  understanding  for 
causality.  For  when,  on  the  one  hand,  we  reflect  that  the 
whole  inorganic  history  of  the  earth  proceeds  in  accordance 
with  mechanical  laws  and  without  any  intervention  by 
creative  power,  and  when,  on  the  other  hand,  we  consider 
that  the  entire  organic  history  of  the  world  is  also  de- 
termined bjT  similar  mechanical  laws  ;  when  we  see  that  no 
supernatural  interference  by  a  creative  power  is  needed  for 
the  production  of  the  various  organisms,  then  it  is  certainly 
quite  inconsistent  to  assume  such  supernatural  creative 
interference  for  the  first  production  of  life  upon  our  globe. 
At  all  events  we,  as  investigators  of  nature,  are  bound 
at  least  to  attempt  a  natural  explanation. 

At  present,  the  much  agitated  question  of  spontaneous 
generation  appears  very  intricate,  because  a  large  number 
of  very  different,  and  in  part  cpaite  absurd,  conceptions  are 

included    under   the   term    "  spontaneous  generation,"    and 

25 


32  THE   EVOLUTION   OF   MAN. 

because  some  have  supposed  that  the  problem  could  be 
solved  by  means  of  the  crudest  experiments.  The  doctrine 
of  spontaneous  generation  cannot  be  experimentally  refuted. 
For  each  experiment  with  a  negative  result  merely  proves 
that  under  the  conditions  (always  very  artificial)  supplied  by 
us,  no  organism  has  been  produced  from  inorganic  combina- 
tions. Neither  can  the  theory  of  spontaneous  generation 
be  experimentally  proved  unless  great  difficulties  are  over- 
come ;  and  even  if  in  our  own  time  Monera  were  produced 
daily  by  spontaneous  generation — as  is  very  possible — yet 
the  absolute  empiric  proof  of  this  fact  would  be  extremely 
difficult — indeed,  in  most  cases  impossible.  He,  however, 
who  does  not  assume  a  spontaneous  generation  of  Monera, 
in  the  sense  here  indicated,  to  explain  the  first  origin  of  life 
upon  our  earth,  has  no  other  resource  but  to  believe  in  a 
supernatural  miracle ;  and  this,  in  fact,  is  the  questionable 
standpoint  still  taken  by  many  so-called  "  exact  naturalists," 
who  thus  renounce  their  own  reason. 

Sir  William  Thomson  has  indeed  tried  to  avoid  the 
necessary  hypothesis  of  spontaneous  generation  by  assuming 
that  the  organic  inhabitants  of  our  earth  originally  de- 
scended from  germs  which  proceeded  from  the  inhabitants 
of  other  planets,  and  which,  with  fragments  of  the  latter, 
with  meteorites,  accidentally  fell  on  to  the  earth.  This 
hypothesis  has  met  with  much  applause,  and  was  even 
supported  by  Helmholtz.  Friederich  Zoellner,  an  acute 
physicist,  has,  however,  refuted  it  in  his  excellent  natural- 
philosophical  work  "  Ueber  die  Natur  der  Cometen,"  a 
critical  book  containing  most  valuable  contributions  to  the 
history  and  theory  of  knowledge.127  Zoellner  has  plainly 
shown  that  the  hypothesis  is  unscientific  in  two  respects — 


MONERA  ALONE  PRODUCED  BY    SPONTANEOUS  GENEEATION.   33 

firstly,  in  point  of  logic,  and  secondly,  in  its  scientific  tenor 
(p.  xxvi).  At  the  same  time  he  rightly  shows  that  the 
hypothesis  of  spontaneous  generation,  in  the  sense  which 
we  have  defined,  is  the  "  condition  necessary  to  the  conceiv- 
ability  of  nature  in  accordance  with  the  laws  of  causality." 

In  conclusion,  I  repeat,  with  emphasis,  that  it  is  only  in 
the  case  of  Monera — of  structureless  organisms  without 
organs — that  we  can  assume  the  hypothesis  of  spontaneous 
generation.  Every  differentiated  organism,  every  organism 
composed  of  organs,  can  only  have  originated  from  an 
undifferentiated  lower  organism  by  differentiation  of  its 
parts,  and  consequently  by  Phylogeny.  Hence,  even  in  the 
production  of  the  simplest  cell  we  must  not  assume  the  pro- 
cess of  spontaneous  generation.  For  even  the  simplest  cell 
consists  of  at  least  two  distinct  constituent  parts ;  the 
inner  and  firmer  kernel  (nucleus),  and  the  outer  and 
softer  cell-substance  or  protoplasm.  These  two  distinct 
parts  can  only  have  come  into  being  by  differentiation  of 
the  homogeneous  plasson  of  a  moneron  and  of  a  cytod.  It 
is  for  this  very  reason  that  the  natural  history  of  Monera  is 
of  the  highest  interest ;  for  it  alone  can  remove  the  principal 
difficulties  which  beset  the  question  of  spontaneous  genera- 
tion. The  extant  Monera  do  afford  us  organless  and  struc- 
tureless organisms,  such  as  must  have  originated  by  spon- 
taneous generation  at  the  first  beginning  of  organic  life 
upon  the  earth.133 


CHAPTER  XVI. 

THE   ANCESTRY   OF   MAN. 
I.  From  the  Moneka  to  the  Gastr^ea 

Relation  of  the  General  Inductive  Law  of  the  Theory  of  Descent  to  the 
Special  Deductive  Laws  of  the  Hypotheses  of  Descent. — Incompleteness 
of  the  Three  Great  Records  of  Creation :  Palasontology,  Ontogeny,  and 
Comparative  Anatomy. — Unequal  Certainty  of  the  Various  Special 
Hypotheses  of  Descent. — The  Ancestral  Line  of  Men  in  Twenty-two 
Stages  :  Eight  Invertebrate  and  Fourteen  Vertebrate  Ancestors. — Distri- 
bution of  these  Twenty-two  Parent-forms  in  the  Five  Main  Divisions  of 
the  Organic  History  of  the  Earth. — First  Ancestral  Stage  :  Monera. — 
The  Structureless  and  Homogeneous  Plasson  of  the  Monera. — Differen- 
tiation of  the  Plasson  into  Nucleus,  and  the  Protoplasm  of  the  Cells. — 
Cytods  and  Cells  as  Two  Different  Plastid-forms. — Vital  Phenomena 
of  Monera.— Organisms  without  Organs. — Second  Ancestral  Stage  : 
Amoebae. — One-celled  Primitive  Animals  of  the  Simplest  and  most  Un- 
differentiated Nature. — The  Amoeboid  Egg-cells. — The  Egg  is  Older  than 
the  Hen. — Third  Ancestral  Stage  :  Syn-Amceba,  Ontogenetically  repro- 
duced in  the  Morula. — A  Community  of  Homogeneous  Amoeboid  Cells.— 
Fourth  Ancestral  Stage  :  Planasa,  Ontogenetically  reproduced  in  the 
Blast  ula  or  Planula. — Fifth  Ancestral  Stage  :  Gastraea,  Ontogenetically 
reproduced  in  the  Gastrula  and  the  Two-layered  Germ-disc— Origin  of 
the  Gastraea  by  Inversion  (invaginatio)  of  the  Planaea. — Haliphysema 
and  Gastrophysema. — Extant  Gastrajads. 

"  Now,  very  probably,  if  the  course  of  evolution  proves  to  be  so  very 
simple,  it  will  be  thought  that  the  whole  matter  is  self-evident,  and  that 
research  is  hardly  required  to  establish  it.  But  the  story  of  Columbus  and 
the  egg  is  daily  repeated ;  and  it  is  necessary  to  perform  the  experiment 


INDUCTIVE   AND   DEDUCTIVE   METHODS.  35 

for  one's  self.  IIow  slowly  progress  is  made  in  the  knowledge  even  of  self- 
evident  matters,  especially  when  respectable  authorities  disagree,  I  myself 
have  experienced  suflicicntly." — Karl  Ernst  Baer  (1828). 

Guided  by  the  fundamental  law  of  Biogeny  and  by  the 
sm*e  records  of  creation,  we  now  turn  to  the  interesting 
task  of  examining  the  animal  parent-forms  of  the  human 
race  in  their  proper  sequence.  To  ensure  accuracy,  we 
must  first  become  acquainted  with  the  various  mental 
operations  which  we  shall  apply  in  this  natural-philosophical 
research.  These  operations  are  partly  of  an  inductive, 
partly  of  a  deductive  nature ;  partly  conclusions  from 
numerous  particular  experiences  to  a  general  law ;  partly 
conclusions  from  this  general  law  back  to  particular  ex- 
periences. 

Tribal  history  as  a  whole  is  an  inductive  science  ;  for 
the  whole  theory  of  descent,  as  an  indispensable  and  most 
essential  part  of  the  whole  theory  of  evolution,  is  entirely 
founded  on  inductions.  From  all  the  biological  incidents  in 
plant  life,  in  animal  life,  and  in  human  life,  we  have  derived 
the  certain  inductive  conception  that  the  whole  of  the  or- 
ganic inhabitants  of  our  globe  originated  in  accordance  with 
one  single  law  of  evolution.  To  this  law  of  evolution,  La- 
marck, Darwin,  and  their  successors  gave  definite  form  in 
the  theory  of  descent.  All  the  interesting  phenomena  ex- 
hibited by  Ontogeny,  Palaeontology,  Comparative  Anatomy, 
Dysteleology,  Chorology,  the  CEkology  of  organisms,  all  the 
important  general  laws,  which  we  infer  from  multitudinous 
phenomena  of  these  different  sciences,  and  which  are  most 
intimately  connected  together,  are  the  broad  inductive 
data  from  which  is  drawn  the  most  extensive  inductive 
law  of  Biology.     Because  the  innate  connection  between  all 


36  THE   EVOLUTION   OF   MAN. 

these  infinitely  various  groups  of  phenomena  in  these  dif- 
ferent departments  becomes  explicable  and  comprehensible 
solely  through  the  theory  of  descent,  therefore  this  theory 
of  evolution  must  be  regarded  as  an  extensive  inductive 
law.  If  we  now  really  apply  this  inductive  law,  and  with 
its  help  seek  to  discover  the  descent  of  individual  organic 
species,  we  must  necessarily  form  phylogenetic  hypotheses, 
which  are  of  an  essentially  deductive  nature,  and  which  are 
inferences  from  the  general  theory  of  descent  back  to  indi- 
vidual particular  cases.  These  special  deductive  conclusions 
are,  however,  in  accordance  with  the  inexorable  laws  of 
Logic,  as  justifiable,  as  necessary,  and  as  indispensable  in 
our  department  of  knowledge  as  the  general  inductive 
conclusions  of  which  the  whole  theory  of  evolution  is 
formed.  The  doctrine  of  the  animal  parent-forms  of  man- 
kind is  al.o  a  special  deductive  law  of  this  kind,  which  is 
the  logical  conclusion  from  the  general  inductive  law  of  the 
theory  of  descent.134 

As  is  now  very  generally  acknowledged,  both  by  the 
adherents  of  and  the  opponents  of  the  theory  of  descent, 
the  choice,  in  the  matter  of  the  origin  of  the  human  race, 
lies  between  two  radically  different  assumptions  :  We  must 
either  accustom  ourselves  to  the  idea  that  all  the  various 
species  of  animals  and  plants,  Man  also  included,  ori- 
ginated independently  of  each  other  b)7"  the  supernatural 
process  of  a  divine  "creation,"  which  as  such  is  entirely 
removed  from  the  sphere  of  scientific  observation — or  we 
arc  compelled  to  accept  the  theory  of  descent  in  its  entirety, 
and  trace  the  human  race,  equally  with  the  various  animal 
and  plant  species,  from  an  entirely  simple  primaeval  parent- 
form.     Between  these  two  assumptions  there  is  no  third 


FAITH   OR   SCIENCE.  37 

course.  Either  a  blind  belief  in  creation,  or  a  scientific 
theory  of  evolution.  By  assuming  the  latter,  and  this  is  the 
only  possible  natural-scientific  conception  of  the  universe, 
we  are  enabled,  with  the  help  of  Comparative  Anatomy  and 
Ontogeny,  to  recognize  the  human  ancestral  line  with  a 
certain  approximate  degree  of  certainty,  just  as.  is  more  or 
less  the  case  with  respect  to  all  other  organisms.  Our 
previous  study  of  the  Comparative  Anatomy  and  Ontogeny 
of  Man,  and  of  other  Vertebrates,  has  made  it  quite  clear 
that  we  must  first  seek  the  pedigree  of  mankind  in  that  of 
the  vertebrate  tribe.  There  can  be  no  doubt  that  (if  the 
theory  of  descent  is  correct)  Man  has  developed  as  a  true 
Vertebrate,  and  that  he  originated  from  one  and  the  same 
common  parent-form  with  all  other  Vertebrates.  This 
special  deduction  must  be  regarded  as  quite  certain,  correct- 
ness of  the  inductive  law  of  the  theory  of  descent  being  of 
course  first  granted.  No  single  adherent  of  the  latter  can 
raise  a  doubt  about  this  important  deductive  conclusion. 
We  can,  moreover,  name  a  series  of  different  forms  of  the 
vertebrate  tribe,  which  may  be  safely  regarded  as  the  repre- 
sentatives of  different  successive  phylogenetic  stages  of 
evolution,  or  as  different  members  of  the  human  ancestral 
line.  We  can  also  prove  with  equal  certainty  that  the 
vertebrate  tribe  as  a  whole  originated  from  a  group  of  low 
invertebrate  animal  forms;  and  among  these  we  can  again 
with  more  or  less  certainty  recognize  a  series  of  members 
of  the  ancestral  chain. 

We  must,  however,  at  once  expressly  say  that  the  cer- 
tainty of  the  different  hypotheses  of  descent,  which  are 
founded  entirely  on  special  deductive  inferences,  is  very 
unequal.     Several   of  these   conclusions   are   already  fully 


38  THE   EVOLUTION    OF   MAN. 

established  ;  others,  on  the  contrary,  are  most  doubtful ;  in 
yet  others,  it  depends  upon  the  subjective  proportion  of  the 
knowledge  of  the  naturalist  and  on  his  capability  of  draw- 
ing conclusions,  what  degree  of  probability  he  will  accord 
to  them.  It  is,  at  all  events,  necessary  thoroughly  to  dis- 
tinguish between  the  absolute  certainty  of  the  general 
(inductive)  theory  of  descent,  and  the  relative  certainty  of 
the  special  (deductive)  hypothesis  of  descent.  We  can 
never  in  any  case  prove  the  whole  ancestral  line  of  an- 
cestors of  an  organism  with  the  same  certainty  with  which 
we  regard  the  theory  of  descent  as  the  only  scientific  expla- 
nation of  the  organic  forms.  On  the  contrary,  the  special 
proof  of  all  separate  parent-forms  must  always  remain 
more  or  less  incomplete  and  hypothetical.  That  is  quite 
natural.  For  all  the  records  of  creation  upon  which  we 
rely  are  in  a  great  measure  incomj)lete,  and  will  always 
remain  incomplete ;  just  as  in  the  case  of  Comparative 
Philology. 

Above  all,  Pakeontology,  the  most  ancient  of  all  records 
of  creation,  is  in  the  highest  degree  incomplete.  "We  know 
that  all  the  petrifications  with  which  we  are  acquainted 
form  but  an  insignificantly  small  fragment  of  the  whole 
number  of  animal  forms  and  plant  forms  which  have  ever 
existed.  For  each  extinct  species  obtained  by  us  in  a  petrified 
condition,  there  are  at  least  a  hundred,  probably  thousands 
of  extinct  species  which  have  left  no  trace  of  their  existence. 
This  extreme  and  most  deplorable  defectiveness  of  the  palpeon- 
tological  record  of  creation,  upon  which  it  is  impossible  to 
insist  too  strongly,  is  very  easily  accounted  for.  The  very 
conditions  under  which  organic  remains  become  petrified 
necessitate  it.     It  is  also  partly  explicable  as  the  result  of 


INCOMPLETENESS  OF   THE   BIOLOGICAL   RECORDS.  39 

an  imperfect  knowledge  in  this  department.  It  must  be 
remembered,  that  far  the  greater  proportion  of  the  rock 
strata  which  constitute  the  mountain  masses  of  the  surface 
of  the  earth  is  not  yet  unfolded  to  us.  Of  the  count- 
less petrifications  which  are  hidden  in  the  huge  moun- 
tain chains  of  Asia  and  Africa,  we  know  but  a  few  small 
samples.  Part  of  Europe  and  of  North  America  has  alone 
been  more  minutely  explored.  The  whole  of  the  petri- 
factions accurately  known  and  in  our  collections  do  not 
amount  to  a  hundredth  part  of  those  which  really  exist  in 
the  crust  of  the  earth.  In  this  respect  we  may,  therefore, 
expect  a  rich  harvest  of  discoveries  in  the  future.  But,  in 
spite  of  this,  the  palseontological  record  of  creation  (for 
reasons  which  I  have  amply  explained  in  Chapter  XV.  of 
my  "Natural  History  of  Creation")  will  always  remain 
extremely  incomplete. 

Not  less  incomplete  is  the  second,  most  important  record 
of  creation,  that  of  Ontogeny.  For  the  Phylogeny  of  the 
individual  it  is  the  most  important  of  all.  Yet,  it  also  has 
its  great  defects,  and  often  leaves  us  in  the  lurch.  In  this 
matter,  we  must  distinguish  quite  clearly  between  palin- 
genetic  and  kenogenetic  phenomena,  between  the  original, 
inherited  evolution  and  the  later,  vitiated  evolution.  We 
must  never  forget  that  the  laws  of  abridged  and  vitiated 
heredity  frequently  disguise  the  original  course  of  evolution 
beyond  recognition.  The  reproduction  of  the  Phylogeny 
in  the  Ontogeny  is  but  rarely  tolerably  complete.  The 
earliest  and  most  important  stages  of  germ-history  are 
usually  the  most  abridged  and  compressed.  The  youthful 
evolutionary  forms  have  in  turn  often  adapted  themselves 
to   new   conditions,   and    have  thus   been    modified.      The 


40  THE   EVOLUTION   OF  MAN. 

struggle  for  existence  has  excited  an  equally  strong  modify- 
ing influence  upon  the  various  independent  and  yet  un- 
developed young  forms,  as  upon  the  developed  and  mature 
forms.  Therefore,  in  the  Ontogeny  of  the  higher  animal 
forms,  the  Phylogeny  has  been  very  greatly  limited  by  Keno- 
genesis  ;  as  a  rule,  only  a  blurred  and  much  vitiated  picture 
of  the  original  course  of  evolution  of  their  ancestors  now 
lies  before  us  in  the  Ontogeny.  Only  with  great  precaution 
and  judgment  dare  we  infer  the  tribal  history  directly  from 
the  germ-history.  Moreover,  the  germ-history  itself  is 
known  to  us  only  in  the  case  of  very  few  species. 

Lastly,  the  highly  important  record  of  creation  afforded 
by  Comparative  Anatomy  is  unfortunately  very  incomplete, 
and  for  the  simple  reason,  that  the  number  of  extant 
animal  species  forms  but  a  very  small  fragment  of  the 
whole  number  of  different  animal  forms  that  have  existed 
from  the  beginning  of  the  organic  history  of  the  world  to 
the  present  time.  The  total  sum  of  the  latter  may  safely 
be  estimated  at  several  millions.  The  number  of  those 
animals  the  organization  of  which  has  at  present  been 
investigated  by  Comparative  Anatomy  is  very  small  in  pro- 
portion. The  more  extended  investigations  of  the  future 
will,  here  also,  open  up  unexpected  treasures. 

In  view  of  this  evident  and  natural  incompleteness  of 
the  most  important  records  of  creation,  we  must  of  course 
take  good  care,  in  the  tribal  history  of  Man,  not  to  lay  too 
great  weight  on  single  known  animal  forms,  nor  with  equal 
certainty  to  consider  all  the  stages  of  evolution  which  come 
under  our  consideration,  as  parent-forms.  On  the  contrary, 
in  hypothetically  arranging  our  ancestral  line,  we  must 
take  good  care  to  remember  that  the  single  hypothetical 


UNEQUAL  VALUE  OF  THE   "ANCESTRAL  STAGES.  4 1 

parent-forms  are  of  very  diverse  values  in  relation  to  the 
certainty  of  our  knowledge.  From  the  few  remarks  which, 
while  speaking  of  the  Ontogeny,  we  made  as  to  the  corre- 
sponding phylogenetic  forms,  it  will  have  been  understood 
that  some  germ-forms  may  with  certainty  be  regarded  as 
reproductions  of  corresponding  parent-forms.  We  recog- 
nized the  human  egg-cell  and  the  parent-cell  which  results 
from  the  impregnation  of  the  latter  as  the  first  and  most 
important  form  of  this  kind. 

From  the  weighty  fact  that  the  egg  of  the  human  being, 
like  the  egg  of  all  other  animals,  is  a  simple  cell,  it  may  be 
quite  certainly  inferred  that  a  one-celled  parent-form  once 
existed,  from  which  all  the  many-celled  animals,  Man  in- 
cluded, developed. 

A  second  very  significant  germ-form,  which  evidently 
reproduces  a  priimTeval  parent-form,  is  the  germ-vesicle 
(Blastula),  a  simple  hollow  sphere,  the  wall  of  which  con- 
sists of  a  single  cell-stratum.  A  third  extremely  import- 
ant form  in  germ-history,  which  may  be  quite  safely  and 
directly  referred  back  to  the  tribal  history,  is  the  true  Gas- 
trula.  This  most  interesting  larval  form  already  exhibits 
the  animal  body  composed  of  two  germ-layers,  and  fur- 
nished with  the  fundamental  primitive  organ,  the  intestinal 
canal.  Now,  as  the  same  two-layered  germ-condition,  with 
the  primitive  rudiment  of  the  intestinal  canal,  is  common  to 
all  the  other  animal  tribes  (with  the  single  exception  of  the 
Primitive  Animals,  Protozoa),  we  may  certainly  from  this 
infer  a  common  parent-form  of  similar  construction  to  the 
Gastrula,  the  Gastnua.  Equally  important  in  their  bearing 
on  the  Phylogeny  of  Man,  are  the  very  important  ontoge- 
netical  form  conditions  which  correspond  to  certain  Worms, 


\2  THE   EVOLUTION    OF   MAN. 

Skull-less  Animals  (Acrania),  Fishes,  etc.,  etc.  On  the  other 
hand,  between  these  quite  certain  and  most  valuable  phylo- 
genetic  points,  great  gaps  in  our  knowledge  unfortunately 
exist,  with  which  we  shall  again  and  again  meet,  and  which 
are  satisfactorily  explained  by  reasons  which  have  already 
been  named,  especially  by  the  incompleteness  of  Palaeon- 
tology, of  Comparative  Anatomy,  and  Ontogeny. 

In  the  first  attempts  to  construct  the  human  ancestral 
line,  which  I  made  in  my  Generelle  Morphologie,  and  in 
the  "  Natural  History  of  Creation,"  I  arranged  first  ten, 
and,  later,  twenty-two  different  animal  forms,  which,  with 
more  or  less  certainty,  may  be  regarded  as  the  animal  an- 
cestors of  the  human  race,  and  which  must  be  looked  upon 
as  in  a  sense  the  most  important  stages  of  evolution  in 
the  long  evolutionary  series  from  the  one-celled  organisms 
up  to  Man.135  Of  these  twenty  to  twenty-two  animal  forms, 
about  eight  fall  within  the  older  division  of  tlie  Inverte- 
brates, while  twelve  to  fourteen  belong  to  the  more  recent 
Vertebrate  division.  How  these  twenty-two  most  important 
parent-forms  in  the  human  ancestral  line  are  distributed 
through  the  five  main  periods  of  the  organic  history  of  the 
earth,  is  shown  in  the  following  Table  (XVI.).  At  least  half 
of  these  twenty-two  stages  of  evolution  (that  is,  the  eleven 
oldest  ancestral  forms)  are  found  within  the  Archilithic 
Epoch,  within  that  first  main  period  of  the  organic  history  of 
the  earth,  which  includes  the  larger  half  of  the  latter,  and 
during  which  probably  only  aquatic  organisms  existed.  The 
eleven  remaining  parent-forms  fall  within  the  four  remaining 
main  Epochs:  three  within  the  Palaeolithic  'Epoch,  three 
within  the  Mesolithic  Epoch,  and  four  within  the  Csenolithic 
Epoch.  In  the  last,  the  Anthropolithic  Age,  Man  already 
existed. 


THE  TWENTY-TWO  ANCESTRAL  STAGES.  43 

If  we  would  now  undertake  the  difficult  attempt  to  dis- 
cover the  phylogenetic  course  of  evolution  of  these  twenty- 
two  human  ancestral  stages  from  the  very  commencement  of 
life,  and  if  we  venture  to  lift  the  dark  veil  which  covers  the 
oldest  secrets  of  the  organic  history  of  the  earth,  we  must 
undoubtedly  seek  the  first  beginning  of  life  among  those 
wonderful  living  beings  which,  under  the  name  of  Monera,  we 
have  already  frequently  pointed  out  as  the  simplest  known 
organisms.  They  are,  at  the  same  time,  the  simplest 
conceivable  organisms ;  for  their  entire  body,  in  its  fully 
developed  and  freely  moving  condition,  consists  merely 
of  a  small  piece  of  structureless  primitive  slime  or  plasson, 
of  a  small  fragment  of  that  extraordinarily  important  nitro- 
genous carbon  compound,  which  is  now  universally  esteemed 
the  most  important  material  substratum  of  all  the  active 
phenomena  of  life.  The  experiences  of  the  last  ten  years 
particularly  have  convinced  us  with  more  and  more  cer- 
tainty that  wherever  a  natural  body  exhibits  the  active 
phenomena  of  life,  nutrition,  propagation,  spontaneous 
movement,  and  sensation,  a  nitrogenous  carbon  compound, 
belonging  to  the  chemical  group  of  albuminous  bodies,  is 
always  active,  and  represents  the  material  substance  through 
which  these  vital  activities  are  effected.  Whether,  in  a 
monistic  sense,  we  conceive  the  function  as  the  direct  effect 
of  the  formed  material  substance,  or,  in  a  dualistic  sense,  we 
regard  "  Matter  and  Force  "  as  distinct,  it  is  at  least  certain 
that,  hitherto,  no  living  organism  has  been  observed  in  which 
the  exercise  of  vital  activities  was  not  inseparably  connected 
with  a  plasson-body.  In  the  Monera,  the  simplest  con- 
ceivable organisms,  the  whole  body  consists  merely  of  plasson, 
corresponding  to  the  "  primitive  slime  "  of  earlier  natural 
philosophy. 


(     44     ) 


TABLE    XVI. 

Systematic  Survey  of  the  most  Important  Stages  in  the  Animal 
Ancestral  Line  of  Man. 

MN  =  Boundary  between  the  Invertebrate  and  the  Vertebrate  Ancestors. 


Epochs  of  the 

Geological  Periods 

Animal 

Nearest 

Organic 

of  the 

Ancestral  Stages 

Living  Relatives 

Histoi  y  of  the 

Organic  History 

of 

of  the 

Earth. 

of  the  Earth. 

Man. 

A  ncestral  Stages. 

1.  Monera 
(Monera) 

2.  Oldest  Amoebaj 

3.  Amoeboid  Societies 
(S'rnammbia) 

4.  Ciliated  plantlUE 

(Planceadre) 

5.  Primitive  Intes- 

! 

\ 

1 

i 
i 

1 

| 

Bathybius 

Protamceba 

Simple  Amoebae 

(Automaba) 

Morula  larva: 
Blastula  larva; 

I. 

tinal  animals 

Gastrula  larvae 

1.  Laurentian  Period 

(Gastrmad  i ) 

1 

Archilithic 

6.  Primitive  Worms 

! 

Gliding  Worms 

or          -> 

2.  Cambrian  Period 

(Archelminthes) 

(Titrbdlaria) 

Primordial 
Epoch 

3.  Silurian  Period 

1.  Soft-worms 
(Scolecida) 

! 

?  Between  the  glid- 
ing worms  and  the 
Sea-squirts 

8.  Chorda  animals 

i 

Sea-squirts  (Ascidiw) 

(Chordoma) 

(Appendicular  i *) 

9.  Skull-less  animals 

j 

Lancelets 

(Acrania) 

i 

(Amphioxi) 

10.  Round-mouths 

t 

'  Lampreys 

(Cycloi-tomi) 

1 

(Petromi/zonta) 

11.  Primitive  Fishes 

» 

Sharks 

(Selachii) 

1 

(Squalacei) 

Devonian  Period 
Coal  Period 
Permian  Period 


12.  Salamander  fishes 
(Uipneusta) 

13.  Gilled  Amphibia 
(Sozobranchin) 

14.  Tailed  Amphibia 
(Soznra) 


Mud  fish 

(Protoptera) 

Siren  (Proteus) 

and  Axolotl 

(SiredonJ 
Water-newt 

(Triton) 


III. 

Mesolithic 

or 

Secondary 

Epoch 


Triassic  Period 
Jurassic  Period 
Chalk  Period 


15.  Primitive  Am- 
niota 
(Protamnia) 
16.  Primitive  Mam- 
mals 
(Promammalia) 
11.  Pouched  Animals 
(Marsupialia) 


t  Between  Tailed 
Amphibians  and 
Beaked  animals 

Beaked  animals 
(Monotrema) 

Pouched  Rats 
(Didelphyes) 


IV. 

Csenolithic 

or 

Tertiary 

Epoch 


Eocene  Period 
Miocene  Period 
Pliocene  Period 


18.  Semi-Apes  i 

(Prosimire)  \ 

19.  Tailed  Narrow-  i 

nosed  Apes  | 

20.  Men-like  Apes  or  i 
Tail-less  Narrow- 
nosed  Api  s.  I 

21.  Speechless  Men  or  t 
Ape-like  Men  '( 


Lori  (Stenops) 
Maki  (Lemur) 
Nose  Apes 
Holy  Apes 
Gorilla,  Chimpan- 
zee, Orang, 
Gibbon 
Cretins  or  Micro- 
cephali 


V. 

Quaternary 
Epoch 


{: 


Diluvial  Period 
Alluvial  Period 


22.  Men     capable    of 
speech 


Australians  and 
Papuans 


MONERON   AND   MORULA.  45 

The  soft  slimelike  plasson-substance  of  the  body  of  the 
Moneron  is  commonly  called  "protoplasma,"  and  identified 
with  the  cell-substance  of  ordinary  animal  and  plant  cells. 
As,  however,  Eduard  van  Beneden,  in  his  excellent  work 
upon  the  Gregarinse,  first  clearly  pointed  out,  we  must, 
strictly  speaking,  distinguish  thoroughly  between  the 
plasson  of  cytods  and  the  protoplasm  of  cells.  This  dis- 
tinction is  of  special  importance  in  its  bearing  on  the  history 
of  evolution.  As  was  before  incidentally  mentioned,  we 
must  assume  two  different  stages  of  evolution  in  those  ele- 
mentary organisms,  which,  as  formative  particles  or  plastids, 
represent  organic  individuality  of  the  first  order.  The  older 
and  lower  stage  is  that  of  the  cytods.  in  which  the  whole  body 
consists  of  but  one  kind  of  albuminous  substance,  of  the 
simplest  plasson  or  formative  material.  The  more  recent 
and  higher  stage  is  that  of  cells,  in  which  a  separation  or 
differentiation  of  the  original  plasson  into  two  different 
kinds  of  albuminous  substances,  into  the  inner  cell-kernel 
(nucleus),  and  the  outer  cell-substance  (protoplasma),  has 
already  taken  place. 

The  Monera  are  the  simplest  permanent  cytods.  Their 
entire  body  consists  merely  of  soft,  structureless  plasson. 
However  thoroughly  we  examine  them  with  the  help  of 
the  most  delicate  chemical  reagents  and  the  strongest  optical 
instruments,  we  yet  find  that  all  the  parts  are  completely 
homogeneous.  These  Monera  are,  therefore,  in  the  strictest 
sense  of  the  word,  "  organisms  without  organs ;  "  or  even,  in 
a  strictly  philosophical  sense,  they  might  not  even  be  called 
"  organisms,"  since  they  possess  no  organs,  since  they  are 
not  composed  of  various  particles.  They  can  only  be  called 
organisms,  in  so  far  as  they  are  capable  of  exercising  the 


46  THE   EVOLUTION    OF   MAN. 

organic  phenomena  of  life,  of  nutrition,  reproduction,  sensa- 
tion, and  movement.  If  we  tried  to  construct,  a  priori,  the 
simplest  conceivable  organism,  we  should  always  be  com- 
pelled to  fall  back  upon  such  a  Monera. 

Although  in  all  real  Monera  the  body  consists  merely 
of  such  a  small  living  piece  of  plasson,  yet,  among  the 
Monera,  which  have  been  observed  in  the  sea  and  in 
fresh  water,  we  have  been  able  to  distinguish  several  dif- 
ferent genera  and  species,  varying  in  the  mode  in  which  their 
tiny  bodies  move  and  reproduce.  In  the  ways  in  which 
movement  is  accomplished  very  noticeable  differences  exist. 


Fig.  163. — A  Moneron  {Protamceba)  in  the  act  of  reproduction :  A,  the 
whole  Moneron,  -which  moves,  like  the  ordinary  Amoeba,  by  means  of  variable 
processes  ;  B,  a  contraction  round  its  circumference  parts  it  into  two  halves  ; 
C,  the  two  halves  separate,  and  each  now  forms  an  independent  individual 
(much  enlarged). 

In  some  Monera,  especially  in  the  Protamceba  (Fig.  163), 
the  formless  body,  during  its  movements,  invariably  de- 
velops only  a  few,  short,  and  blunt  processes,  which  project 
like  fingers,  slowly  altering  their  form  and  size,  but  never 
branching.  In  other  Monera,  on  the  other  hand  (e.g., 
Protomyxa,  Myxastrum),  very  numerous,  long,  fine,  and 
generally  thread-like  processes  arise  from  the  surface  of 
the    movable   body,    and   these    branch    irregularly,   inter- 


THE   BATHYBIUS.  47 

twining  their  free  moving  ends,  so  as  to  form  a  net.     Huge 
masses  of  such  slime-nets  crawl  upon  the  deepest  bottom 
of  the  sea  {Bathybius,  Fig.  164).     Within  these  soft  slime- 
like plasson-nets  slow  currents  continually  pass.     Such  a 
Moneron    may    be    fed   with    finely    pulverized    colouring 
matter   (for   instance,    carmine   or   indigo  powder),  if  this 
powder  is  scattered  in  the  drop  of  water  under  the  micro- 
scope,  in   which    the  Moneron  is  contained.      The  grains 
of  colouring  matter  at  first  adhere  to   the  surface  of  the 
slimy  body,  and  then  gradually  penetrate,  and  are  driven 
about  in  irregular  directions.     The  separate  smallest  par- 
ticles,   or   molecules,   of  the    Moneron-body,   called   "  plas- 
tidules," 136    displace     each     other,    change    their    relative 
positions,  and  thus  effect  a  change  in  the  position  of  the 
absorbed    particles    of  colouring   matter.     This    change    of 
position,  at  the  same  time,  proves  positively  that  a  hidden 
delicate  structure  does  not  exist.     It  might  be  argued  that 
the   Monera   are   not   really   structureless,  but  that   their 
organization  is  so  minute  that,  in  consequence  of  the  in- 
adequate power  of  our  magnifying  glasses,  it  is  invisible. 
This  objection  is,  however,  invalid,  for  by  the  experiment 
of  feeding,  we  can,  at  any  moment,  prove  the  entrance  of 
foreign,  formed,  small  bodies  into  the  different  parts  of  the 
body  of  the  Moneron,  and  that  these  are  irregularly  driven 
about  in  all  directions.     At  the  same  time  we  see  that  the 
changeable  network  of  threads,  formed  by  the  branching 
of  the  protoplasmic  threads  and  the  coalescence  of  the  con- 
fluent branches,   alter   their   configuration  every  moment; 
just  as  has  long  been  known  to  occur  in  the  thread-nets 
of  the  protoplasm  in  the  interior  of  the  plant-cells.     The 
Monera  are,  therefore,  really  homogeneous  and  structureless; 


48  THE   EVOLUTION   OF   MAN. 

each  part  of  the  body  is  every  other  part.  Each  part  can 
absorb  and  digest  nourishment ;  each  part  is  excitable  and 
sensitive  ;  each  part  can  move  itself  independently ;  and 
lastly,  each  part  is  capable  of  reproduction  and  regenera- 
tion. 

The  reproduction  of  Monera  always  occurs  asexually. 
In  the  Protamceba  (Fig.  163),  each  individual,  after  it 
has  grown  to  a  certain  size,  simply  separates  into  two 
pieces.  Round  the  circumference  of  the  body  a  contraction 
arises,  as  in  cell-division.  The  connection  between  the  two 
halves  continually  becomes  more  slender  (B),  and  finally 
parts  in  the  middle.  Thus,  in  the  simplest  possible  way, 
two  new  individuals  proceed  by  self-division  from  one 
quite  simple  individual  (C).  Other  Monera,  after  they  have 
grown  to  a  certain  size,  gather  themselves  together  into  a 
spherical  form.  The  globular  protoplasmic  body  exudes 
a  jelly-like  protecting  envelope,  and  a  breaking-up  of  the 
whole  plasson-ball  takes  place  within  this  covering ;  it 
breaks  either  into  four  pieces  (Vampyrella),  or  into  a 
large  number  of  smaller  globules  (Protomonas,  Protomyxa ; 
cf.  Plate  I.  in  the  "  Natural  History  of  Creation ").  After 
a  time,  these  globules  begin  to  move,  split  the  integument 
by  their  movement,  and  emerge;  after  which  they  float 
about  by  means  of  a  long,  thin,  thread-shaped  process. 
Each  again  passes  by  simple  growth  into  the  mature  form. 
Thus,  it  is  possible  to  distinguish  different  genera  and 
species  of  Monera,  on  one  hand,  by  the  form  of  the  different 
processes  of  the  body,  and,  on  the  other  hand,  by  the 
different  kind  and  manner  of  reproduction.  In  the  appendix 
to  my  monograph  of  the  Monera  I  enumerated  eight  genera 
and  sixteen  species  ("Biol.  Studien,"  vol.  i,  p.   182).     The 


THE  MONERON  AND  BATHYBIUS.  49 

most  remarkable  of  all  Monera  is  the  Bathybius,  which  was 
discovered  by  Huxley  in  1868  (Fig.  164).  This  wonderful 
Moneron  lives  in  the  deepest  parts  of  the  sea,  especially  in 


Fig.  164. — Bathybius  Hasckelii  (Huxley).  A  small  piece  of  the  formless 
and  continually  changing  plasson-net  of  this  Moneron  from  the  Atlantic 
Oceau. 

the  Atlantic  Ocean,  and  in  places  covers  the  whole  floor 
of  the  sea  in  such  masses,  that  the  fine  mud  on  the  latter 
consists,  in  great  measure,  of  living  slime.  The  protoplasm 
in  these  formless  nets  does  not  seem  differentiated  at 
all;  each  little  piece  is  capable  of  forming  an  individual. 
The  active  amoeboid  movements  of  these  formless  pieces  of 
plasson,  which  were  first  observed  by  the  English  zoologists 
Carpenter  and  Wyville  Thomson,  have  recently  been  again 
observed  by  the  German  Arctic  voyager,  Emil  Bessels,  in 
the  Bathybius  of  the  coast  of  Greenland.137 

The  origin   and   importance   of  these   huge   masses  of 
living,  formless  plasson -bodies  in  the  lowest  depths  of  the 


50  THE   EVOLUTION   OF   MAN. 

sea,  raises  many  different  inquiries  and  thoughts.  Spon- 
taneous generation,  especially,  is  naturally  suggested  by  the 
Bathybius.  We  have  already  found  that,  for  the  origin  of 
first  Monera  upon  our  globe,  the  assumption  of  spontaneous 
generation  is  a  necessary  hypothesis.  We  shall  be  all  the 
more  inclined  to  confirm  it  now  that,  in  the  Monera,  we  have 
recognized  those  simplest  organisms,  the  origin  of  which 
by  spontaneous  generation,  in  the  present  condition  of  our 
science,  no  longer  involves  very  great  difficulties.  For  the 
Monera  actually  stand  on  the  very  boundary  between 
organic  and  inorganic  natural  bodies.138 

Next  to  the  simple  cytod-bodies  of  the  Monera,  as  the 
second  ancestral  stage  in  the  human  pedigree  (as  in  that  of 
all  other  animals),  comes  the  simple  cell,  that  most  undifferen- 
tiated cell-form,  which,  at  the  present  time,  still  leads  an 
independent  solitary  life,  as  the  Amoeba.  For  the  first  and 
oldest  process  of  organic  differentiation,  which  affected  the 
homogeneous  and  structureless  plasson-body  of  the  Monera, 
caused  the  separation  of  the  latter  into  two  different  sub- 
stances ;  an  inner  firmer  substance,  the  kernel,  or  nucleus, 
and  an  outer,  softer  substance,  the  cell-substance,  or 
2)rotoplasma.  By  this  extremely  important  separative  pro- 
cess, by  the  differentiation  of  the  plasson  into  nucleus  and 
protoplasm,  the  organized  cell  originated  from  the  structure- 
less cytod,  the  nucleolated  from  the  non-nucleolated  plastid. 
That  the  cells  which  first  appeared  upon  the  earth  origin- 
ated in  this  manner,  by  the  differentiation  of  the  Monera,  is 
a  eonception  which  in  the  present  condition  of  histological 
knowledge  seems  quite  allowable ;  for  we  can  even  yet 
directly  observe  this  oldest  histological  process  of  differ- 
entiation in  Ontogeny.    It  will  be  remembered  that  in  the 


THE   MONERULA. 


51 


egg-cell  of  animals,  either  before  or  after  fertilization,  the 
original  kernel  disappeared.  We  explained  this  phenomenon 
as  a  reversion  or  atavism,  and  assumed  that  the  egg-cell, 
in  accordance  with  the  law  of  latent  heredity,  first  falls 
back  into  the  kernel-less,  cytod  stage  (Fig.  165).  It  is  only 
after  fertilization  is  accomplished  that  a  new  cell-kernel 
arises  in  this  cytod,  which  thus  becomes  the  parent-cell 
(Cytula,  Fig.  106).  The  transitory  kernel-less  cytod-con- 
dition,  intermediate  between  the  egg-cell  and  the  parent- 
cell,  is  an  interesting  germ-form,  because,  in  accordance 
with  the  fundamental  law  of  Biogeny,  it  reproduces  the 
original,  oldest  parent-form  of  the  Moneron ;  we  therefore 
call  it  the  Monerula.     (Cf.  vol.  i.  pp.  178-183.) 


Fig.  1G5.— Monerula  of  Mammal  (Rabbit).  The  fertilized  egg-cell  after 
the  loss  of  the  nucleus  is  a  simple  ball  of  protoplasm  {d).  The  outer  covering 
of  the  latter  is  formed  by  the  modified  zona  pellucida  (z)  together  with 
a  mucous  layer  (h)  secreted  on  to  the  outside  of  the  latter.  In  this  a  few 
sperm. cells  are  still  visible  (s). 

Fir,  166.-Parent.cell  (Cytula)  of  a  Mammal  (Rabbit):  I;  parent, 
kernel ;  n,  nucleolus  of  the  latter ;  p,  protoplasm  of  the  parent-cell ;  e, 
mod.fied  zona  pellucida;  s,  sperm-cells;  h,  outer  albuminous  covering. 


52  THE   EVOLUTION   OF  MAN. 

We  have  already  explained  the  one-celled  germ-form, 
which  we  see  in  the  original  egg-cell  and  the  parent-cell 
which  is  originated  by  the  fertilization  of  the  egg-cell,  as 
the  reproduction  of  a  one-celled  parent-form,  to  which  we 
ascribed  the  organization  of  an  Amoeba  (cf.  Chap.  VI.).  For 
the  Amoeba,  as  it  yet  lives  widely  distributed  in  the  fresh 
and  salt  waters  of  the  globe,  must  be  regarded  as  the  most 
undifferentiated  and  most  original  of  the  various  one-celled 
Primitive  Animals.  As  the  immature  primitive  egg-cells 
(which  as  "  primitive  eggs "  or  Protova  are  found  in  the 
ovary  of  animals)  are  indistinguishable  from  ordinary 
Amoebae,  we  are  justified  in  pointing  to  the  Amoeba  as  the 
one-celled  phylogenetic  form,  which,  in  accordance  with  the 
fundamental  law  of  Biogeny,  is  at  the  present  time  yet 
reproduced  in  the  ontogenetic  primitive  condition  of  the 
"  Amoeboid  e<™-cell."  As  evidence  of  the  striking  cor- 
respondence  of  the  two  cells,  it  was  incidentally  men- 
tioned that  in  the  case  of  some  Sponges  the  real  eggs  of 
these  animals  were  formerly  described  as  parasitic  Anicebse. 
Large  one-celled  Amoeba-like  organisms  were  seen  creeping 
about  in  the  interior  of  the  Sponge,  and  were  mistaken  for 
parasites.  It  was  only  afterwards  that  it  was  discovered 
that  these  "parasitic  Amoebae  "  (Fig.  168)  are  really  the  eggs 
of  the  Sponge,  from  which  the  young  Sponges  develop. 
These  egg-cells  of  the  Sponge  are,  however,  so  like  the 
true  common  Amoebae  (Fig.  167)  in  size  and  structure,  in 
the  nature  of  their  nuclei  and  in  the  characteristic  form  of 
movement  of  their  continually  changing  false-feet  (pseudo- 
podia),  that,  unless  their  source  is  known,  it  is  impossible 
to  distinguish  them. 

This  phylogenetic  explanation  of  the  egg-cell  and  its 


AMCEbLE. 


53 


reference  to  the  primaeval  ancestral  form  of  the  Amoeba, 
directly  enables  us  to  give  a  definite  answer  to  the  old  hu- 
morous riddle:  Which  was  first,  the  egg  or  the  hen?    We  can 


Fig.  167. — A  crawling  Arnoeba  (rnuch  enlarged).  The  whole  organism  has 
the  form-value  of  a  simple  naked  cell  and  moves  about  by  means  of  change- 
able processes,  which  are  extended  from  the  protoplasmic  body  and  again 
drawn  iu.  In  the  inside  is  the  bright-coloured,  roundish  cell-kernel  or 
nucleus. 

Fig.  168.-- -Egg-cell  of  a  Chalk-Sponge  (Ohjnthus).  The  egg-cell  creeps 
about  in  the  body  of  the  Sponge  by  extending  variable  pi'ocesses,  like  those 
of  the  ordinary  Amoeba. 


now  very  simply  answer  this  Sphinx-question,  with  which 
our  opponents  try  to  shake  or  even  to  refute  the  Theory  of 
Evolution.  The  egg  existed  much  earlier  than  the  hen.  Of 
course  it  did  not  exist  in  the  form  of  a  bird's  egg,  but  as  an 
undifferentiated  amoeboid  cell  of  the  simplest  form.  The 
egg  existed  independently  during  thousands  of  years  as  a 
simplest  one-celled  organism,  as  the  Amoeba.  It  was  only 
after  the  descendants  of  these  one-celled  Primitive  Animals 
had  developed  into  many-celled  animal  forms,  and  after 
these  had  sexually  differentiated,  that  the  egg,  in  the  present 
"physiological  sense  of  the  word,  originated  from  the  amoe- 


54  THE   EVOLUTION    OF   MAN. 

boid  cell.  Even  then,  the  egg  was  first  a  Gastrsea-egg,  then 
a  Worm-egg,  then  an  Acrania-cgg,  then  a  Fish-egg,  an  Am- 
phibian-egg, a  Reptile-egg,  and  lastly,  a  Bird-egg.  The  egg 
of  the  Bird,  as  it  now  is,  is  a  most  complex  historical  pro- 
duct, the  result  of  countless  processes  of  heredity,  which 
have  occurred  in  the  course  of  many  millions  of  years.139 

The  fact  that  this  primitive  egg-form,  as  it  first  appears 
in  the  ovary  of  the  most  dissimilar  animals,  is  always  of 
one  form,  an  undifferentiated  cell,  of  the  simplest  amoeboid 
character,  has  already  been  pointed  out  as  an  especially 
important  phenomenon.  In  this  earliest  young  condition, 
immediately  after  the  individual  egg-cell  has  originated  in 
consequence  of  a  separation  of  the  cells  of  the  maternal 
ovary,  no  essential  difference  is  recognizable  in  the  egg-cells 
of  the  most  dissimilar  animals.  (Cf.  Fig.  10,  vol.  i.  p.  134.)  It 
is  not  till  later,  when  the  primitive  egg-cells,  or  the  primitive 
eggs  (protova),  have  absorbed  different  kinds  of  nutritive 
yelk,  and  have  surrounded  themselves  with  variously  formed 
coverings,  and  in  other  ways  differentiated — it  is  not  till 
they  have  in  this  way  changed  into  after-eggs  (metova), 
that  those  of  different  classes  of  animals  can  usually  be 
distinguished.  These  peculiarities  of  the  developed  after- 
egg,  the  mature  egg,  are  naturally  to  be  considered  as  only 
secondarily  acquired,  by  adaptation  to  the  different  con- 
ditions of  existence  both  of  the  egg  itself  and  of  the  animal 
which  forms  the  egg. 

The  two  first  and  oldest  ancestral  forms  of  the  human 
race,  which  we  have  now  considered,  the  Moneron  and  the 
Amoeba,  are,  considered  from  a  morphological  point  of  view, 
simple  organisms  and  individuals  of  the  first  order,  Plastids. 
All  subsequent   stages  in  the  ancestral  chain  are,  on  the 


PRIMORDIAL   EGG-CLEAVAGE. 


55 


other  hand,  compound  organisms  or  individuals  of  higher 
order — social  aggregations  of  a  number  of  cells.  The 
earliest  of  these,  which,  under  the  name  of  Synamcebse, 
we  must  rank  as  the  third  stage  of  our  pedigree,  are  quite 
simple  societies  of  all  homogeneous  undifferentiated  cells ; 
amoeboid  communities.  To  be  certain  as  to  their  nature 
and  origin,  Ave  need  only  trace  the  ontogenetic  product  of 
the  parent-cell  step  by  step.  After  the  cytula  (Fig.  166) 
has  originated,  by  the  re-formation  of  a  cell-kernel,  from 


Fig.  169. — Original  or  primordial  egg-cleavage.  The  parent-cell,  or 
cytula,  which  resulted  from  the  fertilization  of  the  egg-cell,  first  breaks  up, 
by  a  continuous  and  regular  process  of  division,  into  two  cells  (4),  then  into 
four  (B),  then  into  eight  (C),  and,  lastly,  into  very  numerous  cleavage- 
cells  (£>). 

the  Morula  (Fig.  165),  the  parent-cell  breaks  up,  by  repeated 
division,  into  numerous  cells.  We  have  already  minutely 
examined  this  important  process  of 
egg-cleavage,  and  have  found  that  all 
the  various  modes  of  the  latter  are 
modifications  of  a  single  mode,  that 
of  original  or  primordial  cleavage. 
(Cf.  Chap.  VI1L,  p.  188.)  In  the  Ver- 
tebrate line  this  palingenetic  form  of 
egg-cleavage  has  been  accurately  re- 
26 


Fig.  170.— Mulberry- 
germ,  or  morula. 


56  THE   EVOLUTION   OF   MAN. 

tained  to  the  present  time  only  by  the  Amphioxus,  while 
all  other  Vertebrates  have  assumed  a  modified  kenogenetic 
form  of  cleavage.  (Cf.  Table  III.,  vol.  i.  p.  241.)  The  latter 
certainly  originated  at  a  later  period  than  the  former,  and 
the  egg-cleavage  of  the  Amphioxus  is,  therefore,  extremely 
interesting  (vol.  i.  p.  442).  In  this  the  parent-cell  first 
parts  into  two  similar  cells,  the  two  first  cleavage-cells 
(Fig.  169,  A).  From  these,  by  continuous  division,  arise 
4,  8,  16,  32,  64  cells,  etc,  etc.  (Fig.  169).  The  final  result  of 
this  primordial  cleavage  was,  we  found,  the  formation  of  a 
globular  mass  of  cells,  which  was  entirely  composed  of  homo- 
geneous, undifferentiated  cells  of  the  simplest  character 
(Figs.  170,  and  171,  E).  On  account  of  the  resemblance 
which  this  globular  mass  of  cells  bears  to  a  mulberry  or 
blackberry,  we  called  it  the  "  mulberry-germ,"  or  morula. 

This  "morula"  evidently  at  the  present  day  shows  us 
the  many-celled  animal  body  in  the  same  entirely  simple 
primitive  condition  in  which,  in  the  earlier  Laurentian 
primitive  epoch,  it  first  originated  from  the  one-celled 
amoeboid  primitive  animal  form.  The  morula  reproduces, 
in  accordance  with  the  fundamental  law  of  Biogeny,  the 
ancestral  form  of  the  Synamceba.  For  the  first  cell-com- 
munities, which  then  formed,  and  which  laid  the  first 
foundation  of  the  higher  many-celled  animal  body,  must 
have  consisted  entirely  of  homogeneous  and  quite  simple 
amoeboid  cells.  The  earliest  Arnoebse  lived  isolated  hermit 
lives,  and  the  amoeboid  cells,  which  originated  from  the 
division  of  these  one-celled  organisms,  must  also  have  long 
lived  isolated  and  self-dependent  lives.  Gradually,  however, 
by  the  side  of  these  one-celled  Primitive  Animals,  small 
amoeboid    communities  arose,   owing  to  the   fact  that  the 


GERMINATION   OF   A   CORAL. 
A  ]) 


'-..    ^ 


58  THE   EVOLUTION   OF   MAN. 

Fig.  171. — Germination  of  a  coral  (Monoxenia  Darwinii):  A,  monernla  ; 
B,  parent-cell  (cytula)  •  C,  two  cleavage-cells  ;  D,  four  cleavage-cells ;  E, 
nralberiy-germ  (morula)  ;  F,  vesicular  germ  (blastula)  ;  G,  vesicular  germ 
in  section  ;  H,  infolded  vesicular  germ  in  section  ;  J,  gastrula  in  longitu- 
dinal section;  K,  gastrula,  or  cup-germ,  seen  from  the  outside. 


kindred  cells  which  originated  through  division  remained 
united.  The  advantages  which  these  first  cell-societies  had 
in  the  struggle  for  existence  over  the  solitary  hermit  cell 
must  have  favoured  their  progression,  and  have  encouraged 
further  development.  Yet  even  at  the  present  time  several 
genera  of  Primitive  Animals  live  in  the  sea  and  in  fresh 
water,  and  permanently  represent  these  primitive  cell- 
communities  in  their  simplest  form.  Such,  for  instance,  are 
several  species  of  Cystophrys  described  by  Archer,  the 
Rhizopods  described  by  Richard  Hertwig  under  the  name 
of  Microgrornia  socialis,  and  the  Labyrinthulce  which  were 
discovered  by  Cienkowski ;  formless  masses  of  homogeneous 
and  quite  simple  cells.140 

In  order  to  recognize  the  ancestors  of  the  human  races 
which  developed  first  phjdogenetically  from  the  Syn- 
amceba,  we  need  only  continue  to  trace  the  ontogenetic 
modification  of  the  Amphioxus-morula  in  the  next  stages. 
The  first  thing  noticed  is  that  a  watery  fluid  collects  within 
the  solid  globular  cell-mass,  and  the  cells  are  forced 
together  and  driven  out  to  the  periphery  of  the  body 
(Fig.  171,  F,  G ;  Plate  X.  Fig.  9).  The  solid  mulberry-germ 
thus  changes  into  a  simple  hollow  globe,  the  wall  of  which 
is  formed  of  a  single  cell-stratum.  This  cell-stratum  we 
called  the  germ-membrane  (blastoderma),  and  the  hollow 
globe  the  germ-membrane  vesicle  (blastula,  or  blasto- 
sphcera). 


THE   BLASTULA.  59 

The  interesting  blastula  germ-form  is  also  of  great  sig- 
nificance, for  the  modification  of  the  mulberry-germ  into  the 
germ-membrane  vesicle  takes  place  in  the  same  way  in  a 
great  many  animals  of  very  dissimilar  tribes ;  for  instance,  in 
many  Plant-animals  and  Worms,  in  the  Ascidians,  in  many 
Star-animals  (Echinoderma)  and  Soft-bodied  Animals 
(Mollusca),  and  also  in  the  Amphioxus.  In  those  animals, 
however,  in  the  ontogeny  of  which  there  is  no  real  palin- 
genetic  blastula,  this  deficiency  is  evidently  only  the  result 
of  kenogenetic  causes,  of  the  formation  of  a  nutritive  yelk  ; 
and  of  other  conditions  of  embryonic  adaptation.  We  may 
therefore  assume  that  the  ontogenetic  blastula  is  the  repro- 
duction of  a  primaeval  phylogenetic  ancestral  form,  and  that 
all  animals  (with  the  exception  of  the  lower  Primitive 
Animals)  have  originated  from  a  common  parent-form,  the 
structure  of  which  was  essentially  that  of  a  germ-mem- 
brane vesicle.  In  many  lower  animals,  the  evolution  of  the 
blastula  takes  place  not  within  the  egg-coverings,  but  out- 
side this,  free  in  water.  Very  soon  after  this,  each  cell  of 
the  germ-membrane  begins  to  extend  one  or  more  movable, 
hair-like  protoplasmic  processes;  owing  to  the  fact  that 
these  cilia  or  whips  vibrate  in  the  water  the  whole  body 
swims  about  (Fig.  171,  F).  This  vesicular  larva,  the  body- 
wall  of  which  forms  a  cell-stratum,  and  which  rotates  and 
swims  by  means  of  the  united  vibrations  of  the  cilia,  has, 
ever  since  the  year  1847,  been  called  the  planula,  or  ciliated 
larva.  This  designation,  is,  however,  used  by  different 
zoologists  in  different  senses,  and  the  gastrula,  of  which  we 
shall  speak  presently,  has,  especially,  often  been  confused 
with  the  planula.  It  is,  therefore,  more  convenient  to  call 
the  true  planula-form  the  blastula. 


60 


THE    EVOLUTION-    OF    MAN. 


Various  kinds  of  Primitive  Animals,  which  yet  exist 
both  in  the  sea  and  in  fresh  water,  are  formed  essentially 
like  the  blastula,  and  which,  in  a  certain  sense,  may  be  con- 
sidered as  permanent  or  persistent  blastula-forms,  hollow 
vesicles,  the  wall  of  which  is  formed  of  a  single  stratum  of 
ciliated  homogeneous  cells.  These  Planseads,  or  Blastseads, 
as  they  may  be  called,  are  formed  in  the  very  mixed  society 
of  the  Flagellatfe,  especially  the  Vol  voces  (for  instance, 
Synura).  I  noticed  in  September,  1869,  on  the  Island  Gis-Oe, 
on  the  coast  of  Norway,  another  very  interesting  form,  which 
I  named  Magosphcera  planula  (Figs.  172,  173).  The  fully 
developed  body  of  this  forms  a  globular  vesicle,  the  wall  of 
which  is  composed  of  from  thirty  to  forty  vibratory  homo- 
geneous cells,  and  which  swims  about  freely  in  the  sea.    After 


#ii^ 


Fig.  172. — The  Norwegian  Flimmer-ball  (Magosphcera  planula),  swim- 
ming  by  means  of  its  vibratile  fringes  ;   seen  from  the  surface. 

Fig.  173. — The  same,  in  section.  The  pear-shaped  cells  are  seen  bound 
together  in  the  centre  of  the  gelatinous  sphere  by  a  thread-like  process. 
Each  cell  contains  both  a  kernel  and  a  contractile  vesicle. 


FLIMMER-LARV.E.  6 1 

having  reached  maturity  the  society  dissolves.  Each  sepa- 
rate cell  still  lives  a  while  independently,  grows,  and  changes 
into  a  crawling  Amoeba.  This  afterwards  assumes  a  globu- 
lar form  and  encases  itself  by  exuding  a  structureless 
integument.  The  cell  now  has  just  the  appearance  of  a 
common  animal  egg.  After  it  has  remained  for  a  time  in 
this  quiescent  state,  the  cell  breaks  up,  by  means  of  con- 
tinued division,  first  into  2,  then  into  4,  8,  16,  32  cells. 
These  again  arrange  themselves  so  as  to  form  a  globular 
vesicle,  put  forth  cilia,  and  bursting  the  encasing  integu- 
ment, swim  about  in  the  same  Magosphsera-form  from 
which  we  started.  This  accomplishes  the  entire  life-history 
of  this  remarkable  Primitive  Animal.141 

If  we  compare  these  permanent  blastula-forms  with  the 
freely  swimming  Flimmer-larvse  or  planula-condition,  of 
similar  structure,  of  many  other  lower  animals,  we  may 
with  certainty  infer  therefrom  the  former  existence  of  a 
primaeval  and  long-extinct  parent-form,  the  structure  of 
which  was  essentially  like  that  of  the  planula  or  blastula. 
We  will  call  this  the  Plansea,  or  Blastsea.  The  whole  body, 
in  its  fully  developed  condition,  consisted  of  a  simple  hollow 
globe,  filled  with  fluid  or  structureless  jelly,  the  wall  of 
which  formed  a  single  stratum  of  homogeneous  cells, 
covered  with  cilia.  Many  different  kinds  and  species  of 
Plangea-like  Primitive  Animals  must  certainly  have  existed 
and  formed  a  distinct  class  of  Protozoa,  which  we  may  call 
Flimmer-swimmers  (Planceacla).  A  remarkable  proof  of  the 
natural  philosophical  genius  with  which  Karl  Ernst  Baer 
penetrated  into  the  deepest  secrets  of  the  history  of  animal 
evolution,  is  that,  as  early  as  the  year  1828  (ten  years  before 
the  cell-theory  was  established),  he  guessed  the  significance 


62  THE    EVOLUTION   OF   MAN. 

of  the  blastosphsera,  and,  truly  prophetically,  insisted  upon 
it  in  his  classical  "  Entwickelungsgeschichte  der  Thiere  " 
(vol.  i.  p.  223).  The  passage  in  question  says  :  "  The  Anther 
back  we  go  in  evolution,  the  more  do  we  find  a  corre- 
spondence in  very  different  animals.  This  leads  us  to  the 
question  :  Are  not  all  animals  in  the  beginning  of  their 
evolution  essentially  alike,  and  is  there  not  a  primary  form 
common  to  all  ?  As  the  germ  is  the  undeveloped  animal 
itself,  it  is  not  without  reason  that  it  is  asserted  that  the 
simple  vesicular  form  is  the  common  primitive  form  from 
which  all  animals,  not  only  ideally,  but  also  historically, 
develop."  This  latter  sentence  has  not  only  ontogenetic, 
but  also  phylogenetic  significance,  and  is  all  the  more  note- 
worthy because  the  blastula  of  the  most  diverse  animals, 
and  the  constitution  of  its  wall  of  a  single  cell-stratum,  was 
not  then  known.  And  yet  Baer,  hi  spite  of  the  extreme 
deficiency  of  his  empiric  grounds,  ventured  the  bold  state- 
ment: "At  their  first  appearance  all  animals  are  perhaps 
alike,  and  are  merely  hollow  globes." 

Next  to  the  primaeval  ancestral  form  of  the  Planasa,  as 
the  fifth  stage  in  the  human  pedigree,  is  the  Gastrasa,  a  form 
which  arises  from  the  Planoea.  Of  all  ancestral  forms  this, 
as  we  have  already  shown,  is  of  pre-eminent  philosophical 
significance.  Its  former  existence  is  certainly  proved  by  the 
very  important  gastrula,  which  is  met  with  as  a  transitory 
germ-stage  in  the  ontogeny  of  the  most  various  animals 
(Fig.  171, 1,  K).  We  found  that  the  gastrula,  in  its  original, 
palingenetic  form,  is  a  globular,  oval  or  oblong-round  body, 
with  one  axis  which  has  a  simple  cavity  with  one  opening 
(at  one  pole  of  the  axis).  This  is  the  primitive  intestinal 
cavity  with  its  mouth-opening.    The  intestinal  wall  consists 


THE   GASTR^A.  63 

of  two  cell-strata,  which  are,  in  fact,  the  two  primary  germ- 
layers,  the  animal  skin-layer,  and  the  vegetative  intestinal 
layer. 

The  ontogenetic  origin  of  the  gastrula  from  the  blastula 
at  the  present  clay  affords  us  trustworthy  intelligence  as  to 
the  phylogenetic  origin  of  the  Gastrsea  from  the  Plansea. 
We  found  that  on  one  side  of  the  globular  germ-membrane 
vesicle  a  groove-like  depression  begins,  and  this  inversion 
(invaginatio)  becomes  continually  deeper  (Fig.  171,  II).  At 
last  it  is  so  great,  that  the  outer,  inverted  part  of  the  germ- 
membrane,  or  blastoderm,  attaches  itself  closely  to  the  inner, 
uninverted  portion  (Fig.  171,  /).  Now,  if  guided  by  this 
ontogenetic  process,  we  wish  to  conceive  the  phylogenetic 
origin  of  the  Gastraea  in  accordance  with  the  fundamental 
law  of  Biogeny,  we  must  imagine  that  the  one-layered  cell- 
society  of  the  globular  Planaea  began,  especially  at  one  point 
of  its  surface,  to  absorb  nourishment.  At  the  nutritive  point 
on  the  surface  of  the  ball  a  groove-like  depression  was  gra- 
dually formed  by  natural  selection.  The  groove,  which  was 
at  first  quite  shallow,  in  course  of  time  became  continually 
deeper.  The  function  of  nourishing,  of  absorption  of 
nutriment,  and  digestion,  was  soon  limited  to  the  cells 
which  lined  the  groove,  while  the  other  cells  undertook  the 
function  of  movement  and  covering.  Thus  originated  the 
first  division  of  labour  among  the  originally  homogeneous 
cells  of  the  Plansea. 

The  first  result  of  this  earliest  histological  differentia- 
tion was  the  distinction  of  two  different  kinds  of  cells ; 
within  the  hollow  the  nutritive  cells,  without,  on  the  sur- 
face, the  motive  or  locomotive  cells.  The  distinction  of  the 
two  primaiy  germ-layers  was  thus  caused.     The  inner  cells 


64  THE   EVOLUTION    OF    MAN. 

of  the  hollow  formed  the  inner  or  vegetative  layer,  accom- 
plishing the  functions  of  nutrition ;  the  outer  cells  of  the 
covering  formed  the  outer  or  animal  layer,  exercising  the 
functions  of  locomotion  and  covering  the  body.  This 
first  and  oldest  process  of  differentiation  is  of  such  funda- 
mental significance  that  it  deserves  the  deepest  thought. 
When  we  consider  that  the  body  of  the  human  being, 
with  all  its  different  parts,  and  also  the  body  of  all  other 
higher  animals,  originates  from  these  two  simple  primary 
germ-layers,  we  cannot  over-estimate  the  phylogenetic 
significance  of  the  gastrula.  For  in  the  quite  simple  primi- 
tive intestine,  or  the  primitive  intestinal  cavity  of  the 
gastrula  and  its  simple  mouth-opening,  the  first  real  organ 
of  the  animal  body,  in  a  morphological  sense,  is  gained ; 
the  earliest  genuine  organ,  from  which  all  the  other  organs 
have  differentiated  at  a  later  period.  The  whole  body  of 
the  gastrula  is  really  only  a  "  primitive  intestine." 

We  have  already  pointed  out  the  remarkable  agreement 
between  the  palingenetic  gastrula-forms  of  animals  of  the 
most  diverse  classes ;  of  Sponges  (Fig.  174,  A),  Polyps, 
Corals  (Fig.  171,  I),  Medusa,  Worms  (Fig.  175,  B)  Star- 
animals  (Echinoderma,  C),  Articulated  Animals  (Arthro- 
poda,  D),  Soft-bodied  Animals  (Mollusca,  E),  and  Verte- 
brates (F).  All  these  various  forms  of  the  palingenetic 
gastrula  are  much  alike,  and  are  only  distinguished  by  such 
unessential  and  subordinate  peculiarities,  that  the  systematic 
zoologist,  in  his  "  natural  system,"  could  only  represent  them 
as  different  species  of  a  single  genus.  The  various  kenoge- 
netic  gastrula-forms  which  have  been  described  were  also 
referable  to  that  original  palingenetic  form  (vol.  i.  p.  231).  The 
gastrula  proved  to  be  a  germ-form  common  to  all  classes  of 


DEVELOPMENT    OF   THE   GASTR^A. 


65 


animals,  with  the  exception  of  the  Protozoa.  This  highly 
important  fact  justifies  the  inference  in  accordance  with  the 
fundamental   law  of  Biogeny,    that   the  various   ancestral 


Fig.  174 


Fig.  174. — (A)  Gastrula  of  a  Zoophyte  (Gastrophysema),  Haeckel. 

Fig.  175. — (B)  Gastrula  of  a  Worm  (Arrow-worm,  Sagitta).  After  Kowa- 
levskj'. 

Fig.  176.— (0)  Gastrula  of  an  Echinoderm  (Star-fish,  Uraster).  After 
Alexander  Agassiz. 

Fig.  177. — (D)  Gastrula  of  an  Arthropod  (Primitive  Crab,  Nauplius). 

Fig.  178.— (E)  Gastrula  of  a  Mollusc  (Pond-snail,  Limnceus).  After 
Karl  Rabl. 

Fig.  179.— (F)  Gastrula  of  a  Vertebrate  (Lancelot,  Amphioxus)  After 
Kowalevsky. 


66  THE   EVOLUTION   OF   MAN. 

lines  of  all  these  classes  of  animals  have  developed  phylo- 
genetically  from  the  same  parent-form.  This  most  signifi- 
cant primaeval  parent-form  is  the  Gastraea. 

The  Gastrea  was  at  any  rate  already  present  in  the 
sea  during  the  Laurentian  period,  and  by  means  of  its 
vibratory  fringe  hurried  about  in  the  water,  just  like  the 
yet  extant  free-moving  ciliated  gastrulae  of  this  age.  Pro- 
bably the  primaeval  Gastraea,  which  has  been  extinct  for 
many  millions  of  years,  differed  from  the  living  gastrula 
of  the  present  day  only  in  some  unessential  point.  On 
grounds  derived  from  Comparative  Anatomy  and  Ontogeny, 
the  explanation  of  which  would  lead  us  too  far,  we  may 
assume  that  the  Gastraea  had  already  acquired  sexual  re- 
production, and  did  not  only  propagate  its  species  asexually 
(by  division — bud-formation  or  spore-formation),  as  was 
probably  the  case  with  the  four  preceding  ancestral  stages. 
Presumably,  single  cells  of  the  primary  germ-layers  as- 
sumed the  character  of  egg-cells,  others  that  of  fertilizing 
seed-cells.  (Cf.  Chapter  XXV.)  This  hypothesis  is  founded 
on  the  fact  that  sexual  reproduction  is  yet  met  with  in  the 
same  simple  forms  in  the  lowest  Plant- Animals  (Zoophyta), 
especially  in  the  Sponges. 

Two  small  animal  forms  are  especially  interesting  in 
their  bearing  on  this  aspect  of  the  Gastraea  theory.  They 
have  as  yet  been  little  observed,  but  of  all  extant  animals 
they  are  most  nearly  allied  to  the  primaeval  Gastraea,  and 
may  therefore  be  called  "  the  Gastraeads  of  the  present 
day." 142  One  of  these  animals,  Haliphysema  (Figs.  180  and 
181),  has  been  described  by  Bowerbank  as  a  Sponge ;  the 
other,  Gastrophysema,  by  Carter  as  a  Rhizopod  (as  "  Squa- 
mulina").     The  entire  mature  body  of  the  developed  person 


EXTANT   GASTRJfiADS. 


67 

of  Haliphysema  forms  a  most  simple,  cylindrical  or  egg- 
shaped  pouch,  the  wall  of  which  consists  of  two  cell-strata. 
The  cavity  of  the  pouch   is  the  stomach-cavity,  and  the 


Figs.  180,  181. —  Haliphysema  pvimor&iale,  an  extant  Gastrsea-form. 
Fig.  180.  External  view  of  the  whole  spindle-shaped  animal  (attached  by 
its  foot  to  seaweed).  Fig.  181.  Longitudinal  section  of  the  same.  The 
primitive  intestine  (d)  opens  at  its  upper  end  in  the  primitive  month  (m). 
Between  the  whip. cells  (;/)  lie  amoeboid  eggs  (e).  The  skin-layer  (h)  below 
is  encrusted  with  grains  of  sand,  above  with  sponge-spicnles. 


opening  at  the  top   is   the  mouth-opening   (Fig.  181,  m). 
The  two  cell-strata  forming  the  wall  of  the  pouch  are  the 


68  THE    EVOLUTION    OF   MAN. 

two  primary  germ-layers.  These  most  simple  Plant- Animals 
differ  from  the  gastrula  principally  in  the  fact  that  the 
former  are  attached  by  one  end  (that  opposite  to  the  mouth- 
opening)  to  the  bottom  of  the  sea,  while  the  latter  are 
free.  Moreover,  the  cells  of  the  skin-layer  are  coalescent  and 
have  included  many  foreign  bodies,  such  as  sponge-spicules, 
sand-grains,  etc.,  which  serve  to  support  the  body-wall 
(Fig.  180).  The  intestinal  layer,  on  the  other  hand,  con- 
sists merely  of  a  stratum  of  ciliated  cells  (Fig  181,  cl). 
When  the  Haliphysema  is  sexually  mature,  individual  cells 
of  its  entoderm  assume  the  character  of  female  egg-cells ; 
on  the  other  hand,  individual  cells  of  its  exoderm  become 
male  seed-cells  ;  the  fertilization  of  the  former  by  the  latter 


Figs.  182,  183.— Ascula  of  a  Sponge  (Olynthus).  Fig.  182,  from  the  out- 
side ;  Fig.  183,  in  longitudinal  section  :  g,  primitive  intestine ;  o,  primitive 
mouth  ;  >,  intestinal  layer  ;  e,  skin-layer. 


REPRODUCTION    IN    THE    GASTR.EADS.  69 

takes  place  directly  through  the  stomach-cavity.  A  true 
palingenetic  gastrula  (Fig.  174)  develops,  just  as  in  the 
Monoxenia  (Fig.  171),  from  the  fertilized  egg.  This  swims 
about  for  a  time  in  the  sea,  then  attaches  itself,  and  in  this 
state  resembles  a  simple  young-form,  which  occurs  in  the 
course  of  the  evolution  of  many  other  Plant- Animals,  and 
which  is  called  the  ascula  (Figs.  182,  183).  In  consequence 
of  the  absorption  of  foreign  bodies  by  the  exoderm,  it 
becomes  the  Haliphysema. 

When  we  consider  that  there  is  no  other  important 
difference  between  the  free-swimming  gastrula  and  this 
attached,  simplest  Plant-animal,  we  are  fairly  justified  in 
stating  that  in  the  simplest  form  of  Gastrsea  sexual  repro- 
duction must  have  taken  place  in  the  same  way.  In  the 
Gastreeads,  just  as  in  Plant-animals,  both  kinds  of  sexual 
cells — egg-cells  and  sperm-cells — must  have  formed  in  the 
same  person;  the  oldest  Gastrseads  must,  therefore,  have 
been  hermaphrodite.  For  Comparative  Anatomy  shows 
that  hermaphroditism,  that  is,  the  union  of  both  kinds  of 
sexual  cells  in  one  individual,  is  the  oldest  and  original  con- 
dition of  sexual  differentiation ;  the  separation  of  the  sexes 
(Gonochorismus)  did  not  originate  till  a  later  period. 


(     70    ) 

TABLE    XVII. 

Systematic  Survey  of  the  five  earliest  evolutionary  stages  of  the  Human  An- 
cestral Line,  compared  with  the  five  earliest  stages  of  Individual  and 
of  Systematic  Evolution. 


Form-Value 
Of  the  five  earliest 
stages    of   the    animal 
body. 


Phylogeny. 
The     five     earliest 
stages  in  the    evolu- 
tion of  the  tribe. 


First  Stage. 
A  quite  simple  cytod 
(a  non-nucleated  plas- 
tid). 


2. 

Second  Stage. 
A    simple    cell    (a 
nucleated  plastid). 


3. 

Third  Stage. 
A   quite   simple   ag- 
gregation    of     simple, 
similar  cells. 


Fourth  Stage. 
A  simple  hollow  globe, 
filled  with  liquid,  the 
wall  of  which  consists 
of  a  single  stratum  of 
homogeneous  cells. 


5. 

Fifth  Stage. 
A  hollow  body,  with 
a  single  axis,  the  wall 
of  which  consists  of 
different  cell-strata ; 
with  an  opening  at  one 
pole  of  the  axis. 


1. 

Monera. 

The  oldest  animal 
Monera  (originating 
by  spontaneous  gene- 
ration). 


Amoeba. 

Oldest  animal  Amceba. 


3. 
Synamceba. 

The  oldest  aggrega- 
tion of  animal  Amceba?. 


4. 
Planaea. 

An  animal  hollow 
globe,  the  wall  of 
which  consists  of  a 
single  stratum  of 
ciliated  cells. 
(blastaa.) 


5. 
Gastraea. 

Parent-form  of  in- 
testinal animals,  or 
Metazoa.  Simple  pri- 
mitive intestine  with 
primitive  mouth.  The 
body-wall  is  formed 
by  the  exoderm  and 
the  entoderm. 


Ontogeny. 

The  five  earliest 
stages  in  the  evolu- 
tion of  the  germ. 


The  System. 

The  five  earliest 
stages  in  the  animal 
system. 


1. 

Monerula. 
A  non  -  nucleated 
animal-egg  (after  fer- 
tilization and  after 
loss  of  the  germ- 
vesicle). 

2. 
Cytula. 

A  nucleated,  ferti- 
lized animal-egg  ("  first 
cleavage  globule  "). 


3. 
Morula. 
"  Mulberry-germ." 
A  globular  mass  of 
cleavage-cells. 


4. 
Blastula. 

A  hollow  globe,  the 
wall  of  which  consists 
of  a  single  stratum 
of  homogeneous  cells 
(the  Planula  of  lower 
animals). 

(blastosphcera.) 


5. 
Gastrula. 
Intestinal  larva. 
A  simple  intestinal 
cavity  with  a  mouth- 
opening.     The  body- 
wall  is  formed  by  the 
two    primary    germ- 
layers. 


1. 

Monera. 

Protamceba,  Bathy- 
bius,  and  other  extant 
Monera. 


2. 
Amoeba. 

Extant  Amceba. 


3. 

Labyrinthula. 

A  mass  of  similar, 
one  -  celled  primitive 
animals. 


4. 
Magosphaera. 

A  hollow  globe,  the 
wall  of  which  consists 
of  a  single  stratum  of 
homogeneous  ciliated 
cells. 


5. 
Haliphysema. 

A  quite  simple  plant- 
animal.  An  unarticu- 
lated  uniaxial  person, 
the  body-wall  of  which 
consists  of  the  exoderm 
and  the  entoderm. 


.   CHAPTER  XYIL 

THE  ANCESTEAL  SEEIES  OF  MAN. 

II. — From  the  Primitive  Worm  to  the  Skulled  Animal. 

The  Four  Higher  Animal  Tribes  are  descended  from  the  Worm  Tribe. — The 
Descendants  of  the  Gastrsea ;  in  one  direction  the  Parent  Form  of  Plant- 
Animals  (Sponges  and  Sea-Nettles),  in  the  other  the  Parent  Form  of 
Worms. — Radiate  form  of  the  former,  Bilateral  form  of  the  latter. — The 
Two  Main  Divisions  of  the  Worms,  Acoelomi  and  Coelomati :  the  former 
without,  the  latter  with,  a  Body  Cavity  and  Blood-vessel  System. — 
Sixth  Ancestral  Stage  :  Archeluiinthes,  most  nearly  allied  to  Turbellaria. 
— Descent  of  the  Coelomati  from  the  Acoelomi. — Mantled  Animals 
(Tunicata)  and  Chorda-Animals  (Chordonia). — Seventh  Stage:  Soft- 
Worms  (Scolecida). — A  Side  Branch  of  the  latter:  the  Acorn- Worm 
(Balanoglossus) . — Differentiation  of  the  Intestinal  Tube  into  Gill-intes- 
tine and  Stomach-intestine. — Eighth  Stage :  Chorda-Animals  (Chor- 
donia).— Ascidian  Larva  exhibits  the  Outline  of  a  Chorda-Animal. — 
Construction  of  the  Notochord. — Mantled  Animals  and  Vertebrates  as 
Diverging  Branches  of  Chorda- Animals. — Separation  of  Vertebrates  from 
the  other  Higher  Animal  Tribes  (Articulated  Animals,  Star-Animals, 
Soft-bodied  Animals). — Significance  of  the  Metameric  Formation. — 
Skull-less  Animals  (Acrania)  and  Skulled  Animals  (Craniota). — Ninth 
Ancestral  Stage  :  Skull-less  Animals. — Amphioxus  and  Primitive  Verte- 
brate.— Development  of  Skulled  Animals  (Construction  of  the  Head, 
Skull,  and  Brain). — Tenth  Ancestral  Stage  :  Skulled  Animals,  allied 
to  the  Cyclostomi  (Myximoida  and  Petromyzonidof) . 

"  Not  like  the  gods  am  I !     Full  well  I  know  ; 
But  like  the  worm  which  in  the  dust  must  go, 
And,  finding  in  the  dust  his  life  and  weal, 
Is  crushed  and  buried  by  the  traveller's  heel. — 


72  THE    EVOLUTION   OF  MAN. 

Why  dost  thou  grin  at  me,  thou  hollow  skull  ? 

As  though  of  old  thy  brain,  like  mine,  was  vexed, 
Had  looked  to  find  bright  day,  but  in  the  twilight  dull, 

In  search  for  truth,  was  sad  and  sore  perplexed !  " 

Goethe. 

Both  in  prose  and  in  poetry  man  is  very  often  compared 
to  a  worm.  "A  miserable  worm,"  "a  poor  worm,"  are 
common  and  almost  compassionate  phrases.  If  we  cannot 
detect  any  deep  phylogenetic  reference  in  this  zoological 
metaphor,  we  might  at  least  safely  assert  that  it  contains 
an  unconscious  comparison  with  a  low  condition  of  animal 
development  which  is  interesting  in  its  bearing  on  the 
pedigree  of  the  human  race.  For  there  is  no  doubt  that 
the  vertebrate  tribe,  in  common  with  those  of  the  other 
higher  classes  of  animals,  have  developed  phylogenetically 
from  that  multiform  group  of  lower  invertebrate  animals 
which  are  now  called  Worms.  However  closely  we  limit 
the  zoological  significance  of  the  word  "  Worm,"  it  yet 
remains  indubitable  that  a  large  number  of  extinct  Worms 
must  be  reckoned  among  the  direct  ancestors  of  the  human 
race. 

The  group  of  Worms  {Vermes)  is  much  more  limited  in 
the  Zoology  of  the  present  day,  than  was  the  same  class  in 
the  older  Zoology,  which  followed  the  system  of  Linnaeus. 
It,  however,  yet  includes  a  great  number  of  very  diverse 
lower  animals,  which,  phylogenetically,  we  may  regard  as 
the  few  last  living  twigs  of  an  immense  spreading  tree, 
the  trunk  and  main  branches  of  which  have  for  the  most 
part  long  since  died  off.  On  the  one  side,  among  the 
widely  divergent  classes  of  Worms,  are  found  the  parent- 
forms  of  the  four  higher  tribes  of  animals,  the  Molluscs, 
Star-animals,  Articulates,  and  Vertebrates ;  on  the  other  side, 


DEVELOPMENT   OF   WORMS   AND   PLANT-ANIMALS.  73 

several  comprehensive  groups  and  also  single  isolated  genera 
of  Worms  are  to  be  regarded  as  root-suckers  which  have 
sprouted  directly  from  the  rest  of  the  primaeval  family-tree 
of  the  Worms.  Some  of  these  suckers  have  evidently 
changed  but  little  from  the  long-extinct  parent-form,  the 
Primitive  Worm  (Prothelmis),  which  is  immediately  con- 
nected with  the  Gastrsea. 

Comparative  Anatomy  and  Ontogeny  clearly  and  sig- 
nificantly prove  that  the  Gastrsea  must  be  regarded  as 
the  direct  ancestor  of  this  Primitive  Worm.  Even  now,  a 
gastrula  develops  from  the  egg  of  all  Worms  after  its 
cleavage.  The  lowest  and  most  imperfect  Worms  retain 
throughout  life  an  organization  so  simple  that  they  are  but 
little  raised  above  the  lowest  Plant-animals,  which  are  also 
immediate  descendants  of  the  Gastrsea,  and  which  also  yet 
develop  directly  from  the  gastrula.  If  the  genealogical 
relation  of  these  two  lower  animal  tribes,  the  Worms  and 
the  Plant-animals,  is  closely  examined,  it  becomes  evident 
that  the  most  probable  hypothesis  of  their  descent  is,  that 
the  two  originated,  as  independent  branches,  directly  from 
the  Gastrsea.  On  the  one  side,  the  common  parent-form  of 
the  Worms  developed  from  the  Gastrsea ;  as,  on  the  other 
side,  did  the  common  parent-form  of  the  Plant-animals. 
(Of.  Tables  XVIII.  and  XIX.) 

The  tribe  of  Plant-animals  (Zoophytes,  or  Ccelenterata) 
now  comprehends,  on  the  one  side,  the  main  class  of  Sponges 
(Spongice) ;  on  the  other,  the  main  class  of  the  Sea-nettles 
(Acalephce) ;  to  the  former  belong  the  Gastrseads  and 
Poriferse,  to  the  latter  the  Hydroid-polyps,  the  Medusae, 
Ctenophorse,  and  Corals.  From  the  Comparative  Anatomy 
and  the  Ontogeny  of  these  we  may  infer,  with  great  pro- 


74  THE   EVOLUTION   OF   MAN. 

bability,  that  all  these  Plant-animals  descend  from  a 
common  and  very  simple  parent-form,  the  structure  of 
which  resembled  that  of  the  ascula  in  essential  points 
(Figs.  182,  183,  p.  68).  The  uniaxial  outline  of  the  ascula 
and  the  gastrula  is  usually  retained  by  the  Sponges,  while 
in  most  Sea-nettles  (Acalephce)  transverse  axes  have  been 
differentiated  in  the  course  of  further  evolution,  thus  giving 
rise  to  a  characteristic  radiate  structure  with  a  pyramidal 
general  outline. 

In  distinction  from  this  predominant  radiate  outline  of 
Plant-animals,  a  marked  bilateral  general  outline  is  de- 
veloped from  the  first  in  the  second  offshoot  from  the 
gastrula,  in  the  Worms.  As  the  radiate  form  is  marked  by 
adaptation  to  an  adherent  mode  of  life,  so  is  the  bilateral 
form  by  adaptation  to  certain  definite  acts  of  free  loco- 
motion. The  constant  direction  and  carriage  of  the  body 
which  would  be  maintained  in  this  mode  of  free  locomotion, 
conditioned  the  two-sided,  or  bilateral  outline  of  the 
symmetrical  Worms.  Even  the  parent-form  of  the  latter, 
the  Primitive  Worm  (Prothelmis)  must  have  acquired  this 
character,  and  thus  have  become  distinguished  from  the 
uniaxial  parent-form  of  the  Plant-animals.  In  this  simple 
mechanical  impetus,  in  the  defined  free  locomotion  of  the 
Worms,  on  the  one  hand,  and  in  the  stationary  mode  of 
life  of  the  earliest  Plant-animals  on  the  other,  we  must  look 
for  the  efficient  cause  which  produced  in  the  one  the  bi- 
lateral or  two-sided,  in  the  other  the  radiate  outline  of  the 
body.  The  former,  the  bilateral  outline,  has  been  inherited 
by  the  human  race  from  the  Worms. 

Except  through  the  Gastrsea,  the  common  parent-form 
of  Plant-animals  and  Worms,  the  human  race  is,  therefore, 


THE   WORMS   AS   ANCESTORS   OF   MAN.  75 

not  related  to  the  Plant-animals.  It  will  be  our  next  task 
to  consider  more  closely  the  pedigree  of  Man  in  so  far  as 
it  coincides  with  that  of  the  Worms.  Let  us  examine  how 
far  the  Comparative  Anatomy  and  Ontogeny  of  Worms 
justify  us  in  looking  among  the  latter  for  primaeval  ancestors 
of  Vertebrates,  and  therefore  of  Man.  For  this  end  we  must 
first  consider  the  zoological  system  of  Worms.  In  accord- 
ance with  the  most  recent  investigations  of  the  Comparative 
Anatomy  and  Ontogeny  of  Worms,  we  divide  (without 
reference  to  the  many  and  various  peculiarities  of  the 
numerous  separate  classes,  which  in  this  place  do  not 
interest  us)  the  whole  mass  of  forms  within  this  tribe 
into  two  large  main  groups.  The  first  main  group,  which 
we  call  Bloodless  Worms  (Accelomi),  comprehends  the 
earlier  division  of  the  lower  Worms,  which  have  no  true 
body-cavity,  no  system  of  blood-vessels,  no  heart,  no  blood, 
— in  short,  none  of  the  parts  connected  with  this  organ- 
system.  The  second  main  group,  on  the  contrary,  called 
Blood-worms  (Ccelomati),  are  distinguished  from  the  former 
by  the  possession  of  a  true  body-cavity,  and  also  by  the 
presence  of  a  blood-like  fluid,  which  fills  this  cavity ; 
most  of  them  also  develop  special  blood-vessels,  which 
again  cause  further  correlated  advances  in  structure.  The 
relation  of  these  two  main  groups  of  Worms  is  very  evi- 
dently phylogenetic.  The  Accelomi,  which  are  very  nearly 
allied  to  the  Gastrcea  and  the  Plant-animals,  are  to  be 
regarded  as  an  earlier  and  lower  group,  from  which  the 
more  recent  and  higher  division  of  the  Ccelomati  developed, 
perhaps  towards  the  end  of  the  Laurentian  Period. 

We   will   first    carefully   examine   the    lower   group    of 
Worms,  the  Accelomi,  among  which  we  must  look  for  the 


j6  THE   EVOLUTION    OF   MAN. 

sixth  ancestral  stage  of  the  human  race,  the  stage  imme- 
diately following  the  gastrula.  The  name  "  Accelomi  " 
signifies  "  Worms  without  a  body-cavity,  or  coeloma,"  and 
therefore  without  blood,  or  vascular  system.  The  extant 
Accelomi  are  generally  included  in  a  single  class,  which,  on 
account  of  their  flattened  bodies,  are  called  Flat-worms 
(Plathehninthes).  To  this  class  belong  the  Gliding-worms 
(Turbellaria),  which  live  independently  in  the  water ;  also 
the  parasitic  intestinal  Sucking-worms  (Trematoda),  and 
the  Tape-worms  (Cestoda),  which  have  become  yet  more 
degraded  by  parasitism.  The  phylogenetic  relations  of  the 
three  forms  of  Flat- worms  are  very  evident ;  the  Sucking- 
worms  originated  from  the  free  Gliding-worms  by  adaptation 
to  a  parasitic  mode  of  life  ;  and,  by  a  yet  more  completely 
parasitic  life,  the  Tape-worms  originated  from  the  Sucking- 
worms.  These  are  striking  examples  of  the  gradually 
increasing  degeneration  of  the  most  important  organs. 

In  addition  to  these  well-known  extant  Flat-worms, 
great  numbers  of  other  Accelomi  must  have  lived  during 
the  Archilithic  Epoch,  which  in  general  form  were  very 
much  like  those  of  the  present  day,  but  were,  in  some 
respects,  yet  more  simply  organized,  and  were,  in  their 
lowest  stages  of  development,  immediately  connected  with 
the  Gasteeads.  The  whole  of  these  lowest  Accelomi,  among 
which  the  common  parent-form  of  the  whole  Worm  tribe 
(the  Prothelmis)  must  have  been,  may  be  classed  as  "  Primi- 
tive Worms  "  (Archelminthes). 

The  two  classes  of  the  Accelomi,  the  Primitive  Worms 
and  the  Flat-worms,  represent  in  their  external  form  the 
simplest  bilateral  condition  of  the  animal  body.  The 
body  is  a  simple   oval,  usually  somewhat  flattened,  with- 


BLOODLESS   WORMS.  JJ 

out  any  appendage  (Figs.  184,  185).  The  dorsal  side  of 
the  leaf-like  body  differs  from  the  ventral  side,  on  which 
the  Worm  creeps.  Accordingly,  even  in  these  most  simple 
Worms  there  are  the  three  definite  axes  which  mark  the 
bilateral  type-form,  and  which  re-occur  in  the  human 
body  and  in  that  of  all  higher  animals  :  (1)  a  longitudinal 
axis  (main  axis),  which  passes  from  front  to  rear;  (2) 
a  lateral  axis,  passing  from  right  to  left ;  and  (8)  a 
sagittal  axis,  passing  from  the  dorsal  to  the  ventral  surface. 
(Cf.  vol.  i.  p.  257.)  This  so-called  symmetrical  or  "  bilateral" 
arrangement  of  the  outline  of  the  body  is  simply  the 
mechanical  result  of  adaptation  to  a  creeping  form  of  loco- 
motion, during  which  one  end  of  the  body  is  always  directed 
forwards.  The  geometric  outline  of  the  gastrula,  as  of  the 
ascula,  has  but  one  axis  with  unequal  poles  (Monaxonia 
diplopola).  The  typical  outline  of  Worms,  as  of  Vertebrates, 
is,  on  the  contrary,  bilateral,  with  tranverse  axes  (Stau- 
raxonia  dijoleura).lu 

The  whole  outer  surface  of  the  Gliding-worms  (Turbel- 
laria)  is  covered,  as  in  the  gastrula,  with  a  thick,  fine 
ciliated  coat ;  that  is,  with  a  fur-like  covering  of  extremely 
fine  and  close  microscopic  hairs,  which  are  direct  processes 
of  the  uppermost  cells  of  the  epidermis,  and  maintain  an 
uninterrupted  whirling  or  vibratory  motion  (Fig.  184,/). 
The  constant  vibrations  of  these  cilia  cause  a  continued 
current  of  water  over  the  surface  of  the  body.  Fresh  water 
is  constantly  conveyed  to  the  surface  of  the  skin  by  this 
current,  thus  permitting  respiration  in  its  simplest  form  (skin- 
respiration).  A  similar  ciliated  covering,  just  as  is  seen  in 
the  extant  Gliding-worms  of  our  fresh-water  seas,  pre- 
sumably covered   our   extinct   ancestors    of  the    Primitive 


7  8  THE   EVOLUTION   OF   MAN. 

Worm  group,  the  Archelrninthes.  They  inherited  this 
ciliated  dress  directly  from  the  Gastrsea. 

If  we  now  make  various  vertical  sections  (longitudinal 
and  transverse)  through  the  simple  body  of  the  Gliding- worms 
(and  that  of  the  Arclielmitvthes  which  are  certainly  very 
closely  allied  to  the  former),  we  soon  discover  that  their 
internal  structure  is  considerably  higher  than  that  of  the 
Gasteeads.  We  first  observe  that  the  two  primary  germ- 
layers  (inherited  from  the  Gastrsea)  have  differentiated  into 
several  cell-strata.  The  skin-layer  and  the  intestinal  layer 
have  each  split  into  two  strata.  The  four  secondary  germ- 
layers,  which  are  thus  produced,  are  the  same  that  we  found 
resulted  from  the  first  differentiation  of  the  two  primary 
germ -layers  in  the  embryo  of  the  Vertebrate  also.  (Cf.  the 
transverse  sections  through  the  larval  Amphioxus  and 
Earth-worm,  Figs.  50  and  51,  p.  236,  and  Plate  IV.  Fig.  2; 
Plate  V.  Fig.  10.) 

The  highly  important  histological  differentiation  of  these 
four  secondary  germ-layers  led  directly  to  further  organolo- 
gical  processes  of  differentiation,  by  which  the  organism  of 
the  Primitive  Worms  was  soon  considerably  raised  above 
that  of  the  Gasteeads.  In  the  latter  there  was  really,  in 
a  morphological  sense,  but  a  single  organ,  the  primitive  intes- 
tine, with  its  mouth-opening.  The  whole  body  was  nothing 
but  an  intestinal  canal ;  the  intestinal  wall  was  at  the 
same  time  the  wall  of  the  body.  Of  the  two  cell-layers, 
forming  this  intestinal  wall,  the  inner  accomplished  the 
functions  of  nutrition,  the  outer  those  of  motion  and 
covering.  As  some  of  the  cells  of  the  primary  germ -layers 
developed  into  egg-cells,  and  others  into  sperm-cells,  these 
layers  also  performed  the  function  of  reproduction.     In  the 


GLIDING- WORMS.  79 

Primitive  Worms,  however,  simultaneously  with  the  forma- 
tion of  the  secondary  germ-layers,  these  various  functions 
also  beo-an  to  be  distributed  to  various  organs,  which  detached 
themselves  from  the  original  main  organ,  the  primitive  in- 
testine. Special  organs  originated  for  reproduction  (sexual 
glands),  for  secretion  (kidneys),  for  motion  (muscles),  and 
for  sensation  (nerves  and  sense-organs). 

In  order  to  obtain  an  approximate  picture  of  the  sim- 
plest form  in  which  all  these  various  organs  first  appeared 
in  the  Primitive  Worms,  it  is  only  necessary  to  examine 
the  most  imperfect  forms  of  Gliding-worms  (Turbellaria),  as 
they  exist  at  the  present  time  in  salt  and  fresh  water.  They 
are  mostly  very  small  and  insignificant  Worms  of  the  simplest 
form,  many  being  scarcely  a  millimetre  or  a  few  millimetres  in 
length.  In  the  simplest  species  of  Gliding- worms  the  greater 
part  of  the  oval  body  is  occupied  by  the  intestinal  canal. 
This  is  a  very  regularly  shaped  pouch  with  an  opening,  re- 
presenting both  mouth  and  anus  (Fig.  184,  m).  At  the 
anterior  section  of  the  intestinal  tube,  which  is  separated 
as  a  throat  (pharynx,  sd),  the  fibrous  layer  is  very  thick, 
a  thick  muscular  layer.  Immediately  outside  the  intestinal- 
fibrous  layer  lies  the  skin-fibrous  layer,  which  in  most 
worms  appears  as  a  large  skin-muscle  sac.  Above  the 
throat  in  Gliding- worms  a  nerve  system  of  the  simplest 
form  is  already  visible  in  front,  a  pair  of  small  nerve- 
knots,  or  ganglia,  which  from  their  position  are  called  the 
"  upper  throat  ganglia,"  or  "  brain  "  (Fig.  185,  g).  Delicate 
nerve-threads  (n)  pass  from  this  to  the  muscles  and  to  the 
ciliated  skin-sensory  layer.  A  pair  of  quite  simple  eyes 
(ait)  and  nose-pits  (no)  are  to  be  found  in  a  few  Gliding- 
worms.  The  Flat-worms  are  also  universally  provided  with 
27 


8o 


THE   EVOLUTION   OF   MAN. 


a  pair  of  simple  kidney-canals  (  "  excretory  organs  "  ),  in 
the  form  of  two  long,  thin,  glandular  tubes,  which  traverse 
the  right  and  left  sides  of  the  intestine  and  open  at  the 
hinder  end  of  the  body  (Fig.  184<,  nm).     We  found  that  the 


Fig.  184. — A  simple  Gliding- worm  (Rhabdoccelum):  m, mouth;  sd,  throat- 
epithelium  ;  sm,  throat.muscles  ;  d,  stomach-intestine  ;  nc,  kidney  ducts ; 
nm,  opening  of  the  kidneys;   an,  eye  ;   na,  nose-pit. 

Fig.  185. — The  same  Gliding-worm,  showing  the  remaining  organs  :  g, 
brain;  an,  eye;  na,  nose-pit;  n,  nerves;  h,  testes;  £ ,  male  opening; 
?.  female  opening;  e,  ovary  ;  /,  ciliated  outer-skin. 


STRUCTURE   OF   THE   GLIDING-WORMS.  8 1 

two  primitive  kidney  canals  in  the  vertebrate  embryo 
also  appeared  at  a  very  early  period,  shortly  after  the  first 
differentiation  of  the  middle  germ-layer  (mesodermal).  The 
appearance  of  these  at  so  early  a  period  shows  that  the 
kidneys  are  very  important  primordial  organs.  It  also 
shows  their  universal  existence  in  all  Flat- worms  ;  for  even 
the  Tape-worms,  which,  in  consequence  of  the  adoption  of  a 
parasitic  mode  of  life,  have  lost  the  intestine,  yet  have  the 
two  secreting  primitive  kidneys,  or  "  excretory  ducts."  The 
latter  seem,  therefore,  to  be  older  and  of  greater  physiologi- 
cal importance  than  the  blood-vessel  system,  which  is  wholly 
wanting  in  the  Flat- worms.  The  sexual  organs  appear 
in  many  of  the  Gliding- worms  in  a  very  complex  form ; 
while  in  others  their  form  is  very  simple.  Most  of  them 
are  hermaphrodites ;  that  is,  each  individual  worm  has 
both  male  and  female  sexual  organs.  In  the  simplest 
forms  we  find  a  testis  in  the  anterior  part  (Fig.  185,  A), 
a  single  or  double  ovary  behind  (a).  One  of  these  simplest 
existing  Acoelomi,  such  as  we  find  among  the  lowest  Rhab- 
doccela,  may  give  us  an  approximate  idea  of  the  structure 
of  the  Primitive  Worm,  which  forms  the  sixth  stao;e  in 
the  human  pedigree. 

These  ancestors  of  the  human  race,  which,  on  account 
of  their  general  organization,  must  be  placed  among  the 
Bloodless  Worms  (Acoelomi),  must  have  been  represented 
during  the  Archilithic  Epoch  by  a  large  number  of  various 
Worm  forms.  The  lowest  of  these  must  have  been  directly 
connected  with  the  Gastrseads  (the  fifth  ancestral  stage);  the 
most  highly  developed  must,  on  the  other  hand,  have  been 
directly  connected  with  the  Coelomati  (the  seventh  stage). 
As,  however,  our  present   knowledge    of  the  Comparative 


82  THE   EVOLUTION   OF   MAN. 

Anatomy  and  Ontogeny  of  the  Accelomi  is  very  fragmen- 
tary, and  much  too  imperfect  to  enable  us  to  point  with 
certainty  to  the  series  of  the  various  stages,  we  will  not 
attempt  a  detailed  arrangement  of  them.  We  will  turn 
instead  to  the  seventh  stage  in  the  human  pedigree,  which 
belonged  to  the  multiform  group  of  the  Blood-bearing 
Worms  (Coelomati). 

The  great  organic  advance  in  structure  by  which  the 
Blood-bearing  worms,  or  Coelomati,  developed  from  the 
older  Bloodless  Worms,  or  Accelomi,  consisted  in  the  for- 
mation of  a  body-cavity  (cceloma),  and  of  a  nutritive  juice 
filling  the  latter,  the  first  blood.  All  the  lower  animals 
with  which  we  have  yet  occupied  ourselves  in  our  Phy- 
logeny,  all  the  Primitive  Animals  and  Plant-animals,  are, 
like  the  Accelomi,  bloodless  and  without  a  body-cavity.  In 
the  formation  of  a  special  vascular  system,  the  earliest 
Coelomati  made  a  very  great  advance.  Much  of  the  com- 
plexity in  the  organic  structure  in  the  four  higher  tribes  of 
animals  is  based  on  the  differentiation  of  the  vascular 
system,  which  they  have  inherited  from  the  Blood-bearing 
Worms. 

The  first  development  of  a  true  body-cavity  (cceloma) 
is  referable  to  the  separation  of  the  two  fibrous  layers ;  to 
the  formation  of  a  spacious  cavity  between  the  outer  skin- 
fibrous  layer  and  the  inner  intestinal-fibrous  layer.  In  the 
fissure-like  gaps,  which  formed  between  the  two  germ-layers, 
a  juice  collected,  which  penetrated  through  the  intestinal 
wall.  This  juice  was  the  first  blood,  and  the  gaps  between 
the  two  germ-layers  formed  the  first  rudiment  of  the  body- 
cavity.  The  union  of  these  gaps  formed  the  simple  ccelom, 
the  large  cavity,  containing  blood  or  lymph,  which  plays  so 


BLOOD-BEARING   WORMS.  83 

important  a  part  in  all  the  higher  animals  as  the  receptacle 
of  the  very  extensive  intestines.  The  formation  of  this 
coelom,  and  of  the  blood-vessels  developed  in  connection  with 
it,  exercised  a  very  great  influence  on  the  further  evolution 
of  the  animal  organization.  The  most  important  result  was, 
that  it  allowed  the  conveyance  of  rich  nutritive  juices  to 
those  parts  of  the  body  lying  near  the  circumference,  and 
developing  at  a  considerable  distance  from  the  intes- 
tinal canal.  The  intimate  correlation,  or  reciprocity  of  the 
parts,  necessarily  occasioned,  in  direct  connection  with  the 
progressive  development  of  the  blood-vessel  system,  many 
other  important  advances  in  the  structure  of  the  body  of 
the  Blood-bearing  Worms. 

Just  as  among  the  Acoelomi,  so  also  among  the  Coelomati, 
the  pedigree  of  our  race  must  have  passed  through  a  large 
number  of  diverse  ancestral  stages.  But  amonq;  extant 
Coelomati  (which  form  but  a  very  small  fraction  of  this  once 
multiform  group),  there  are  but  very  few  Worms  which  can 
with  certainty  be  regarded  as  nearly  allied  to  the  long- 
extinct  ancestors  of  Man.  In  this  respect,  but  a  single 
class  of  Coelomati  is  really  of  prominent  importance  ;  these 
are  the  Mantled  Animals  (Tunicata),  to  which  belong  the 
Ascidia  already  known  to  us.  Our  careful  examination  of 
the  structure  and  germ-history  of  the  Ascidian  and  the 
Amphioxus  have  shown  the  extreme  importance  of  these 
very  interesting  animal  forms.  (Cf.  Chapters  XIII.  and 
XIV.)  That  examination  fully  justifies  us  in  asserting 
that  among  the  ancestors  of  the  Vertebrates  (and  therefore 
of  Man)  there  was  an  unknown  extinct  coelomate  species, 
to  which  the  nearest  allied  form  among  extant  aniuals  is 
the  Appendicularia   (Fig.  187),  of  which  we   have  already 


84  THE   EVOLUTION   OF  MAN. 

spoken,  and  the  tailed  Ascidian  larva.  We  will  for  the 
present  call  this  kind  of  Worm,  which  was  primarily  dis- 
tinguished by  the  possession  of  a  notochord,  the  Chorda- 
animal  (Chordoniuwi).  The  Ascidians  on  the  one  hand,  and 
the  Vertebrates  on  the  other,  developed,  as  two  diverging 
branches,  from  these  Chorda-animals.  The  common  parent- 
form  of  the  Chorda-animals  themselves  was  a  ccelomate  form, 
which  finally  must  have  descended  from  the  Accelomi,  and 
from  the  Archelminthes. 

Many  connecting  intermediate  forms  must,  of  course,  have 
existed  between  these  two  groups  of  Worms,  between  the 
Primitive  Worms  and  the  Chorda-animals.  Unfortunately, 
however,  zoological  knowledge  is  at  present  especially  im- 
perfect with  regard  to  these  important  intermediate  forms 
of  the  multiform  Worm  tribe.  For  very  evident  reasons, 
none  of  these  Worms  could  leave  fossil  remains.  For,  like 
the  great  majority  of  other  Worms,  they  had  no  hard  parts 
in  their  bodies.  Most  even  of  the  known  fossil  Worms 
are  worthless,  for  they  tell  us  little  or  nothing  of  the  most  im- 
portant structural  features  of  the  soft  body.  Fortunately, 
however,  we  can  in  great  measure  satisfactorily  fill  the  con- 
siderable palseontological  gap  in  this  part  of  our  pedigree, 
with  the  help  of  the  Comparative  Anatomy  and  Ontogeny  of 
Worms.  If,  on  the  one  hand,  we  examine  the  structure  and 
mode  of  development  of  the  lower  Worms  from  the  Gliding- 
Worms  (Turbellaria),  and,  on  the  other  hand,  the  Anatomy 
and  Ontogeny  of  the  Ascidians,  it  is  not  difficult,  step  by 
step,  to  re-construct  in  imagination  the  connecting  inter- 
mediate forms,  and  to  insert  a  series  of  extinct  ancestral 
forms  between  the  Acoelomi  and  the  Chordoma.  This 
series  of  forms  under  the  name  of  Soft-worms  (Scolecida) 


DEVELOPMENT   OF   CHORD  A- ANIMALS.  85 

we    will   consider   as    the    seventh    stage    in    the    human 
pedigree. 

An  examination  of  the  Comparative  Anatomy  of  the 
various  Scolecid  forms,  which  we  might  perhaps  distinguish 
here,  would  lead  us  much  too  far  into  the  difficult  details 
of  the  Comparative  Anatomy  and  Ontogeny  of  the  Worms. 
For  our  purpose  it  seems  more  important  to  call  attention 
to  those  phylogenetic  advances,  by  means  of  which  the 
organization  of  the  earliest  Blood-bearing  Worms  was  in 
the  end  elevated  to  that  of  the  Chorda-animals.  The  Com- 
parative Anatomy  and  Ontogeny  of  the  Gliding-worms 
and  of  the  Ascidians  justify  us  in  giving  special  weight  to 
the  significant  differentiation  of  the  intestinal  canal  into  two 
distinct  divisions ;  into  an  anterior  division  (the  gill-intes- 
tine), which  accomplishes  respiration,  and  a  posterior  divi- 
sion (the  stomach -intestine),  which  accomplishes  digestion. 
As  in  Gastrceads  and  Primitive  Worms,  so  also  in  the  Ascidian 
larva,  the  intestinal  canal  is  at  first  a  simple  pouch-like 
body,  provided  merely  with  a  mouth-opening.  A  second 
opening,  the  anus,  does  not  develop  till  a  later  period.  Gill- 
openings  afterwards  appear  in  the  anterior  section  of  the 
intestinal  canal,  by  which  the  whole  anterior  intestine  is 
transformed  into  a  gill-body.  This  remarkable  arrange- 
ment is,  as  we  found,  quite  peculiar  to  Vertebrates,  and, 
except  in  the  Ascidians,  occurs  nowhere  else.  Among  extant 
Worms  there  is,  however,  a  single  isolated  and  very  remark- 
able Worm  form,  which  in  this  respect  may  be  regarded 
as  distantly  allied  to  the  Ascidia  and  to  Vertebrates,  and 
perhaps  as  an  off-shoot  from  the  Soft-worms  (Scolecida). 
This  is  the  so-called  "Acorn- worm"  {Balanoglossus,  Fig. 
186),  which  lives  in  the  sand  of  the  sea-shore.      The  in- 


86 


THE   EVOLUTION   OF   MAN. 


fceresting  points   connecting  this   with   Asciclians  and   the 

"Skull-less  Animals  (Acrania) 
were  first  accurately  observed 
and  explained  by  Gegenbaur.  Al- 
though this  singular  Balanotrlossus 
is  in  many  other  respects  peculiar 
in  its  organization,  so  that  Gegen- 
baur rightly  ranked  it  as  the  re- 
presentative of  a  special  class 
(EnteropTbeusta),  yet  the  structure 
of  the  anterior  section  of  the  in- 
testinal tube  is  exactly  similar  to 
that  of  Ascidians  and  Skull-less 
Animals  (Jc),  a  gill  body,  the  walls 
of  which  are  pierced  on  either  side 
by  gill-openings  and  are  supported 
by  gill-arches.  Now,  although  the 
Acorn- worm  in  other  points  of  its 
structure  may  differ  very  con- 
siderably from  those  extinct  Soft- 
worms  (Scolecidoe),  which  we  must 
regard  as  direct  ancestors  of  our 
race,  and  as  intermediate  links 
between     the    Primitive    Worms 

Fig.  186. — A  young  Acorn-woi'm  (Bal- 
anoglossus).  (After  Alexander  Agassiz.) 
r,  acorn-like  proboscis;  h,  collar;  k,  gill 
openings  and  gill-arches  of  the  anterior  in- 
testine, in  a  long  row  one  behind  another 
on  each  side ;  d,  digestive  posterior  intes- 
tine, filling  the  greater  part  of  the  body- 
cavity  ;  v,  intestinal  vessel,  lying  between 
two  parallel  folds  of  skin  ;  a,  anus. 


SOFT-WORMS.  87 

and  the  Chorda-animals,  yet,  in  virtue  of  this  characteristic 
structure  of  the  gill-intestine,  it  may  be  considered  a  re- 
motely allied  collateral  line  of  the  Soft-worms.  The 
development  of  an  anus  (Fig.  186,  a)  at  the  end  opposite 
to  the  mouth,  is  also  a  considerable  advance  in  the  struc- 
ture of  the  intestine.  The  further  development  of  the 
blood-vessel  system  in  the  Acorn-worm  also  indicates  a 
marked  advance.  In  the  ciliary  surface  of  the  skin,  on 
the  contrary,  it  recalls  the  Gliding-worms.  The  sexes  are 
separated,  while  our  scolecid  ancestors  were  probably 
h  e  r  maph  rod  ite  ,145 

From  a  branch  of  the  Soft- worms,  the  group  of  Chorda- 
animals  (Chordonia),  the  common  parent-group  of  the 
Mantle-animals  and  Vertebrates  also  developed.  The  process 
which  primarily  led  to  the  development  of  this  important 
group  of  the  ccelomati,  was  the  formation  of  the  inner 
axial  skeleton  (the  notochord,  or  chorda  dorscdis),  which 
at  the  present  day  we  find  permanently  retained  in  its 
simplest  form  in  the  lowest  Vertebrate,  the  Amphioxus. 
We  saw  that  this  notochord  is  already  found  in  the  tailed 
and  free-swimming  larva  of  the  Ascidian  (Plate  X.  Fig.  5). 
The  chorda  does,  indeed,  serve  specially  as  a  support  for 
the  rudder-like  tail  of  the  larval  Ascidian,  but  its  anterior 
extremity  passes  in  between  the  intestinal  and  medullary 
tubes  within  the  actual  body  of  the  larva.  A  transverse 
section  of  this  larva  therefore  shows  that  arrangement  of 
the  most  important  organs  wdiich  is  characteristic  of  the 
vertebrate  type :  in  the  centre  is  the  firm  notochord,  which 
supports  the  other  organs  and  serves  especially  as  a  base 
and  point  of  attachment  for  the  motive  trunk  muscles  ; 
above  this   notochord,  on    the   dorsal   side,  is   the   central 


88  THE   EVOLUTION   OF   MAN. 

nervous  system  in  the  form  of  a  medullary  tube ;  below,  on 
the  ventral  side,  is  the  intestinal  tube,  the  anterior  half  of 
which  is  a  respiratory  gill-intestine,  its  posterior  half  a 
digestive  stomach-intestine.  It  is  true  that  the  free- 
swimming  larva  of  the  extant  Ascidian  possesses  this  typical 
vertebrate  character  only  for  a  short  time ;  it  soon  relin- 
quishes its  free  roving  mode  of  life,  puts  off  its  oar-like  tail 
with  the  notochord,  adheres  to  the  bottom  of  the  sea,  and 
then  undergoes  that  very  great  retrogression,  the  surprising 
final  result  of  which  we  have  already  observed  (Chapters 
XIII.  and  XIV.).  Nevertheless,  the  Ascidian  larva,  in  its 
very  transitory  evolution  (for  a  brief  space),  affords  us  a 
picture  of  the  long  extinct  Chordona-form,  which  must 
be  regarded  as  the  common  parent-form  of  Mantle-animals 
and  Vertebrates.  There  is  even  yet  extant  a  small  and 
insignificant  form  of  Mantle-animal  which  throughout  life 
retains  the  structure  of  the  Ascidian  larva  with  its  oar- 
like tail  and  its  free-swimming  mode  of  life,  and  which 
reproduces  itself  in  this  form.  This  is  the  remark- 
able Appendicularia  (Fig.  187),  which  we  have  already 
examined. 

If  we  ask  ourselves  what  conditions  of  adaptation  could 
possibly  have  had  so  remarkable  a  result  as  the  develop- 
ment of  the  notochord,  and  the  modification  of  a  branch 
of  the  Soft-worms  into  the  parent-form  of  the  Chorda- 
animals,  we  may  with  great  probability  answer,  that  this 
result  was  effected  by  the  habituation  of  the  creeping 
Soft-worm  to  a  swimming  mode  of  life.  By  energetic  and 
continued  swimming  movements,  the  muscles  of  the  trunk 
would  be  greatly  developed,  and  a  strong  internal  point  of 
attachment   would   be   very   favourable   to    this   muscular 


THE  ASCIDIANS.  89 

activity.  A  support  of  this  kind  might  arise  by  enlarge- 
ment and  concrescence  of  the  germ-layers  along  the  longi- 
tudinal axis  of  the  body;  and  the  differentiation  of  an 
independent  bony  cord  from  this  axial  cord  gave  rise  to  the 
notochord.  (Cf.  Fig.  88,  89,  vol.  i.  pp.  300,  301.)  In  corre- 
lation to  the  formation  of  this  central  notochord,  the  simple 
nerve-ganglia,  lying  over  the  throat  in  the  Soft-worms, 
lengthened  into  a  long  nerve-cord,  reaching  from  front  to 
rear,  above  the  notochord ;  in  this  way,  the  medullary  tube 
originated  from  the  "  upper  throat  ganglia." 

As  we  have  already  minutely  considered  the  great 
significance  of  the  Ascidians  (Fig.  188)  in  this  respect,  as 
well  as  their  close  relations  to  the  Amphioxus  (Fig.  189), 
we  will  not  tarry  longer  over  this  point  now.  I  will 
repeat,  that  we  must  by  no  means  regard  the  Ascidian 
as  the  direct  parent-form  of  the  Amphioxus  and  of  the 
other  Vertebrates.  On  the  contrary,  we  assert  that,  on 
the  one  hand  the  Ascidians,  and  on  the  other  the  Ver- 
tebrates, have  both  descended  from  one  unknown 
Worm  form,  which  has  long  been  extinct ;  the  nearest 
relatives  of  this  among  existing  animals  are  the  Ascidian 
larvae  and  the  Appendicularia  (Fig.  187).  This  unknown 
common  parent-form  must  have  belonged  to  the  group  of 
Chorda-animals,  which  we  pointed  out  as  the  eighth 
ancestral  stage  in  the  human  pedigree.146  Although  we 
cannot  form  an  entirely  satisfactory  idea  as  to  all  points 
of  external  and  internal  structure  of  this  Chorda-animal, 
there  is  no"  doubt  that,  like  its  near  relatives,  the 
Mantle-animals,  and  like  the  preceding  ancestral  stage 
represented  by  the  Soft-worms  and  Primitive  Worms,  it 
must  be   classified   in   the   natural   system    of  the   animal 


90 


THE   EVOLUTION    OF   MAN. 


kingdom  as  a  genuine  Worm.     The   difference  between  it 
and  other  genuine  Worms  cannot  have  been  greater  than  is 


Fig.  187. — Appendicularia,  seen  from  the  left  side  :  m,  mouth  ;  k,  gill- 
intestine  ;  o,  oesophagus  ;  vt  stomach ;  a,  anus ;  n,  nerve-ganglia  (upper 
throat-knots) ;  g,  ear-vesicle  ;  /,  ciliated  groove  under  the  gill ;  h,  heart ; 
t,  testes ;  e,  ovary  ;  c,  notochord ;  s,  tail. 

Fig.  188. — Structure  of  an  Ascidian  (seen  from  the  left,  as  in  Fig.  153 
and  Fig.  14,  Plate  XL)  :  sb,  gill-sac ;  v,  stomach ;  i,  large  intestine ;  c, 
heart;  t,  testes ;  vd,  seed-duct;  o,  ovary;  o',  matured  eggs  in  the  body, 
cavity.     (After  Milne  Edwards.) 


THE   AMPI1I0XUS. 


91 


fc 


the  difference  between  the  extant  Tape-worms  and  Ringed 
Worms  (Annelida).  Moreover,  in  a  certain  sense  we  may 
regard  the  extant  Appendicularia  as  a  last  remnant  of  the 
Chordoma  class. 

We  have  now  studied  the  most  import- 
ant animal  forms  which  occur  in  the  pedigree 
of  the  human  race,  and  which,  in  the  zoo- 
logical system,  must  be  classed  among  the 
Worms.  In  leaving  this  lower  class,  and 
tracing  our  ancestry  henceforth  exclusively 

within   the    vertebrate    tribe,  we   at   once       , 

a 

leave  behind  the  great  majority  of  animal 

11, 
forms,  which  branched  off  from  the  worm 

tribe  in  entirely  different  directions.    When, 

in  a  previous  chapter  (IX.),  the  vertebrate    / 

nature  of  man  was  proved,  it  was  incidentally 

mentioned  that  the  very  great  majority  of     •* 

animals  are  in  no  way  directly  allied  to  our      t 

tribe.     The  parent-forms  of  the  three  other      " 

higher  Animal  tribes,  the  Articulated  Animals 

(Arthropocla),  Star-animals  (Eckinoderiaa), 

and   Soft-bodied   Animals  (Mollusca),   like 

the   vertebrate  tribe,    originated   from    the 

Fig.  1S9. — Lancelet  (Amphioxus  lanceolatus),  twice 
the  actual  size,  seen  from  the  left  (the  longitudinal 
axis  is  represented  vertically,  the  month  turned  up- 
ward, the  tail  downward,  as  in  Plate  XL  Fig.  15)  : 
a,  mouth-opening,  surrounded  by  cilia  ;  b,  anal  open- 
ing ;  c,  ventral  opening  (Poms  abdominalis) ;  d,  gill- 
body  ;  e,  stomach  ;  /,  liver- coecum  ;  g,  large  intes- 
tine ;  h,  coelom :  r,  notochord  (under  it  the  aorta)  ; 
k,  arches  of  the  aorta  ;  1,  main  gill-artery  ;  w,  swellings 
on  its  branches ;  n,  hollow  vein ;  0,  intestinal  vein. 


(     92     ) 


TABLE    XVIII. 

Systematic   Survey  of  the  Phylogenetic  System  of  the  Animal  Kingdom, 
founded  on  the  Gastrsea  Theory  and  the  Homology  of  the  Germ-layers. 


Tribes  or  Phyla 

of  the 

Animal  Kingdom. 


Main  Classes  or 

Branches  of  the 

Animal  Kingdom. 


Classes 

of  the 

Animal  Kingdom. 


Systematic  Karnes 
of  the 
Classes. 


First  Sub.kingdom  :  Primitive  Animals  (Protozoa) 
Animals  without  germ-layers,  intestine,  or  true  tissues. 

A.  (        I.  Egg-animals         '    L  Monera  L  Monera 

■Prtmtttbe  Ovularia 


\i 


2.  Amoebae  2.  Lobosa 

_.  Gregarina?  3.  Gregarinaa 

SallUttalS        j  jj   Infusorial  animals  (    4.  Sucking  Infusoria  4.  Acinetas 

Protozoa         \  Infusoria  \    5.  Ciliated  Infusoria  5.  Ciliata 

Second  Sub-kingdom  :  Intestinal  Animals  (Metazoa). 
Animals  with  two  primary  germ-layers,  intestines  and  tissues 

6.  Primitive    intestinal      6.  Gastrasada 
animals 

7.  Sponges 

8.  Corals 
Hood-jellies 

10.  Comb-jellies 

Primitive  worms 


B. 
Pant* 

Snhnals 
Zoophytes 


III.  Sponges 
Spongics 

IV.  Sea-nettles 
Acalephm 


1 10. 


C. 

tEElorms 
Vermes 


D. 
.Soft.faofjirrj 

Animals 
Mollusca 

E. 

Star^mmals 
Echinoderma 

F. 

®rtirulatr& 

Animals 

Arthropoda 


G. 

Urrtdbtatc 

Animals 

Vertebrata 


V.  Bloodless  worms 
Acaloma 


VI.  Blood-worms 
Cmlomati 


fll. 

(  12.  Flat-worms 
/13.  Round-worms 

14.  Arrow-worms 

15.  Wheel-animalcules 

16.  Moss-polyps 

17.  Mantle-animals 

18.  Acorn-worms 

19.  Star-worms 

20.  Ringed-worms 


/  2 

\  22.  Mussels 

J  23. 


Snails 
Cuttles 


Acephala 

VIII.  Head-bearing 

shell-fish 

Eucephala 

IX.  Ringed-arms 
Colobrachia 
X.  Armless 
Lipobrachia 

XL  Gill-breathers 
Carides 

m  ESS"- J  a  as- 


r  25.  Sea-stars 
I  26.  Sea-lilies 
f  27.  Sea-urchins 
I  28.  Sea-cucumbers 


[29.  Crabs 


7.  Porifera 

8.  Coralla 

9.  Hydromedusa? 

10.  Ctenophora 

11.  Archelminthes 

12.  Plathelminches 

13.  Nemathelminthes 

14.  Chcetognathi 

15.  Rotatoria 

16.  Bryozoa 

17.  Tunicate 

18.  Enteropneusta 

19.  Gephyrea 

20.  Annelida 

21.  Spirobranchia 

22.  Lamellibranchia 

23.  Cochlides 

24.  Cephalopoda 

25.  Asterida 

26.  Crinoida 

27.  Echinida 

28.  Holothuriae 

29.  Crustacea 

30.  Arachnida 

31.  Myriopoda 

32.  Insecta 


XIII.  Skull-less 

Acrania 

XIV.  Single-nostrilled 

Monorrhina 

XV.  Amnion-less 
Anamnia 


I  32.  Flies 

<  33.  Tube-hearts  (Lance-    33.  Leptocardia 


lets) 
34.  Round-mouths 

(Lampreys) 
j  35.  Fishes 

36.  Mud-fish 
{ 37.  Amphibians 


XVI.  Amnion-animals  I  3g"  g^.'  eS 
Amniota  \  AQ   Mammal8 


34.  Cyclostoma 

35.  Pisces 

36.  Dipneusta 

37.  Amphibia 

38.  Reptilia 

39.  Aves 

40.  Mammalia 


(    93     ) 
TABLE   XIX. 


Monophyletic  Pedigree  of  the  Animal  Kingdom,  founded  on  the   Gastrsea 
Theory  and  the  Homology  of  the  Germ-layers.24 


c  -a 
.5 -a 


e   g   t- 

B|  o 

tc-  to 


o-^ft 


'£  .=  §  go 
•««  ~.  H  h 


S  r;  s  m 
£  i-  =  eS 

S  =  >  PM 
=  3 


§! 


Articulates 
Arthropoda 


Vertebrates 

Vertebrata 


Star-animals 
Echinoderma 


Soft-bodied  Animals 

Mollusca 


Ccelomati. 

(  Worms  with,  body-cavity') 


Plant-animals 
Zoophyta 
(CozUnterata) 


Sponges 
Spongiae 


Sea-nettles 
(Acalephm) 


Flat  AVorms 
Plathelminiues 


Gastrsea  radialis 
{stationary) 


Acoelomi 
{Worms  witliout  body-cavity) 


Prothelmis 


Gastra'a  bilateralis 
(crawling) 


Gastraea 
(Ontogeny:  (Sastrula) 


§■3.9 


^  3 


s  * 

<  2> 
%   s 


Primitive  Animals 
Protozoa 


Plana'ada 
(Ontogeny :  Ulaslula) 


Ciliata 


Synamceba 
(Ontogeny :  Morula) 


Amoebae 

(Ontogeny :  Cyti(la) 


Monera 
(Ontogeny:   Monerula) 


.94  THE   EVOLUTION   OF   MAN. 

worm  tribe ;  but  the  parent-forms  of  the  three  former 
belong  to  worm-groups  quite  distinct  from  that  of  the 
Chordoma.  It  is  only  far  down  at  the  common  root  of  the 
group  of  Coelomati,  that  we  assume  a  common  source  for 
these  various  tribal  forms.  (Cf.  Tables  XVIII.  and  XIX.) 
It  is  especially  necessary  to  remember  that  there  is  no 
direct  blood-relationship  between  Vertebrates  and  Articu- 
lated Animals. 

The  Articulated  Animals  (Arthropoda),  to  which  the 
most  comprehensive  of  all  classes  of  animals,  that  of  Insects, 
and  also  the  Spiders,  Centipedes,  as  well  as  the  Crabs,  or 
Crustaceans,  belong,  are  descendants  of  articulated  Worms, 
the  nearest  allies  of  which  are  the  extant  Ringed  Worms 
{Annelida).  The  tribe  of  Star-animals  (Echinoderma), 
which  includes  the  Star-fishes,  Sea-lilies,  Sea-urchins,  and 
Sea-cucumbers,  must  also  have  descended  from  similar  articu- 
lated Worms.118  The  parent-form  of  the  Soft-bodied  Animals 
(Mollusca),  which  include  the  Cuttles,  Snails,  Mussels,  and 
Lamp-shells,  must  also  be  sought  among  the  Worms.  But 
the  Coelomati,  from  which  these  three  higher  animal  tribes 
originated,  differed  entirely  in  character  from  the  Chorda- 
animals.  Unlike  the  latter,  they  never  developed  a  noto- 
chord.  In  them,  the  anterior  section  of  the  intestinal  tube 
was  never  modified  into  a  gill-body  with  gill-openings ;  nor 
were  the  upper  throat-ganglia  developed  into  a  medullary 
tube.  In  a  word,  in  Articulated  Animals,  Star-animals,  and 
Soft-bodied  Animals,  as  well  as  in  their  ancestors  among 
the  Blood-bearing  Worms,  the  typical  structural  peculiari- 
ties which  are  exclusively  characteristic  of  the  vertebrate 
tribe  and  of  their  immediate  invertebrate  progenitors,  were 
never  present.      Thus  the  great  majority  of  all  animals  are 


DEVELOPMENT  OF  VERTEBRATES  FROM  INVERTEBRATES.  95 

in  no  way  the  subject  of  our  further  investigations,  which 
are  only  concerned  with  the  Vertebrates. 

The  development  of  the  Vertebrates  from  the  Inverte- 
brates most  nearly  related  to  them,  the  Chorda- Animals, 
occurred  millions  of  years  ago,  during  the  Archilithic  Epoch. 
(See  Table  XII.,  p.  11.)  This  is  unmistakably  shown  by 
the  fact  that  the  most  recent  sedimentary  rock-strata 
which  were  deposited  during  that  immense  period  of  time, 
the  higher  layers  of  the  Upper  Silurian  formation,  contain 
remains  of  fossil  Fishes  (Primitive  Fishes,  Selachii).  As 
these  Fishes,  although  they  belong  to  the  lowest  stage  of 
the  Skulled  Animals  (Craniota),  yet  possess  a  compara- 
tively high  organization,  and  as  they  must  necessarily  have 
been  preceded  by  a  long  progressive  series  of  lower  Skull- 
less  Vertebrates,  we  must  attribute  the  origin  of  the  oldest 
Skull-less  Animals  (Acrania)  from  the  Chorda-animals  to 
a  much  earlier  part  of  the  Archilithic  Epoch.  Therefore, 
not  only  all  the  invertebrate  ancestors  of  our  race,  but  also 
the  earliest  form  of  our  vertebrate  progenitors  must  have 
developed  in  that  primordial  time,  which  includes  the 
Laurentian,  Cambrian,  and  Silurian  Periods.  (Cf.  Tables 
XIII,  XIV.,  and  XVI.,  pp.  12,  19,  44.) 

Unfortunately,  Palaeontology  can  give  us  absolutely  no 
information  with  regard  either  to  the  structure  of  our  oldest 
vertebrate  ancestors,  or  to  the  time  of  their  appearance ; 
for  their  bodies  were  as  soft  and  as  destitute  of  hard 
parts  capable  of  fossilization,  as  were  the  bodies  of  all 
our  preceding  invertebrate  ancestors.  It  is,  therefore,  not 
surprising,  but  quite  natural,  that  we  find  no  fossil 
remains  of  the  former  in  the  Archilithic  formations.  The 
Fishes  in  which  the  soft  cartilaginous  skeleton  was  partly 


96  THE   EVOLUTION   OF   MAN. 

modified  into  hard  bone,  are  the  earliest  Vertebrates  capable 
of  leaving  petrified  records  of  their  existence  and  structure. 

Fortunately,  this  want  is  more  than  counterbalanced 
by  the  much  more  important  testimony  of  Comparative 
Anatomy  and  Ontogeny,  which  henceforth  form  our 
safest  guides  within  the  Vertebrate  pedigree.  Thanks  to 
the  classic  researches  of  Cuvier,  Johannes  Muller,  Huxley, 
and  especially  of  Gegenbaur,  we  are  in  possession  of  such 
extensive  and  instructive  records  of  creation  in  this  most 
important  branch  of  tribal  history,  that  we  can  prove  at 
least  the  more  significant  features  in  the  development  of  our 
Vertebrate  ancestors,  with  the  most  gratifying  certainty. 

The  characteristic  peculiarities  by  which  Vertebrates 
in  general  are  distinguished  from  all  Invertebrates,  engaged 
our  attention  some  time  ago,  when  we  examined  the  structure 
of  the  ideal  Primitive  Vertebrate  (Figs.  52-56,  p.  256).  The 
most  prominent  characters  were  as  follows:  (1)  the  formation 
of  the  notochord  between  the  medullary  and  intestinal  tubes; 
(2)  the  differentiation  of  the  intestinal  tube  into  an  anterior 
gill-intestine  and  a  posterior  stomach-intestine ;  (3)  the 
inner  articulation,  or  formation  of  metamera.  The  Verte- 
brates share  the  first  two  qualities  with  the  larval  Ascidians 
and  with  the  Chorda-animals  ;  the  third  quality  is  entirely 
peculiar  to  them.  Accordingly,  the  most  important  struc- 
tural advance,  by  which  the  earliest  vertebrate  forms  origin- 
ated from  the  most  nearly  allied  Chorda-Animals,  consisted 
in  an  internal  metameric  structure.  This  showed  itself 
first  most  distinctly  in  the  articulation  of  the  muscular 
system,  which  broke  up  on  the  right  and  left  into  a  series 
of  consecutive  muscular  plates.  At  a  later  period  the 
articulation  declared  itself  prominently  in  the  skeleton,  and 


CLASSIFICATION   OF   VERTEBRATES.  97 

nervous  and  blood-vessel  systems.  As  we  have  already 
seen,  this  process  of  articulation,  or  metameric  formation, 
must  essentially  be  regarded  as  terminal  germination. 
Each  distinct  trunk-segment,  or  metameron,  represents  an 
individual.  Thus  the  Vertebrates  with  their  internal 
segmentation  stand  in  a  similar  relation  to  their  inarticulate 
Invertebrate  ancestors,  the  Chorda  Animals,  as  do  the  out- 
wardly segmented  Ringed  Worms  (Annelida)  and  Articu- 
lated Animals  (Arthropoda)  to  the  simple  inarticulate 
Worms  from  which  they  originated. 

The  tribal  history  of  Vertebrates  is  rendered  much  more 
intelligible  by  the  natural  classification  of  the  tribe  which 
I  proposed  first  in  my  Generelle  Morphologic  (1806),  and 
afterwards  improved  in  many  ways  in  "  The  Natural  History 
of  Creation"  (Chap.  XX.,  p.  192,  etc.).  In  accordance  with 
that,  existing  Vertebrates  must  be  divided  into  at  least 
eight  classes,  as  follows  : — 

SYSTEMATIC     SURVEY     OF     THE     EIGHT     CLASSES     OF 
VERTEBRATES. 

A.  Skull-less  {Acrania)  1.  Tube-hearted      1.  Leptocardia 

!a.  Single-nostrilled  (Monorhina)  2.  Round-mouths  2.  Cyclostoma 

/  I.  [3.  Fishes  3.  Pisces 

I  Amnion-less  J  4.  Mud-fishes  4.  Dipneusta 

b.  Double-no'-trilled     I  Anamnia  1 5.  Amphibians  5.  Amphibia 

Amphirhtrta         \  u  ( 6.  Reptiles  6.  Reptilia 

I  With  Amnion  ]  7.  Birds  7.  Aves 

\  Amnivta  (8.  Mammals  S.  Mammalia 

The  whole  Vertebrate  tribe  may  primarily  be  divided 
into  the  two  main  sections  of  the  Skull-less  and  the 
Skulled  Vertebrates.  Of  the  earlier  and  lower  section,  that 
of  the  Skull-less  (Acrania),  the  Amphioxus  is  alone  extant. 
To  the  more  recent  and  higher  section,  the  Skulled  (Cra- 
niota),  belong  all  other  existing  Vertebrates  up  to  Man.    The 


98  THE   EVOLUTION   OF  MAN. 

Craniota  branched  off  from  the  Acrania,  as  these  did  from 
the  Chorda  Animals.  Our  exhaustive  study  of  the  Compara- 
tive Anatomy  and  Ontogeny  of  the  Ascidian  and  the 
Amphioxus  have  already  afforded  proof  of  this  relation.  (Cf. 
Chapters  XIII.  and  XIV.,  and  Plates  X.  and  XI.  with  the 
explanations.)  I  will  only  repeat,  as  the  most  important 
fact,  that  the  Amphioxus  develops  from  the  egg  in  exactly 
the  same  way  as  the  Ascidian.  In  both,  the  original  Bell- 
gastrula  (Figs.  4  and  10)  originates  in  an  exactly  similar 
manner,  by  primordial  cleavage  from  the  simple  parent-cell 
(Figs.  1  and  7).  From  this  originates  that  remarkable  larva, 
which  develops  a  medullary  tube  on  the  dorsal  side  of  the 
intestinal  tube,  and  between  the  two  a  notochord.  At  a 
later  period,  both  in  the  Ascidian  and  in  the  Amphioxus,  the 
intestinal  tube  differentiates  into  an  anterior  gill-intestine 
and  a  posterior  stomach-intestine.  In  accordance  with  the 
fundamental  principle  of  Biogeny,  from  these  very  important 
facts  we  may  deduce  the  following  statement  of  great  phylo- 
genetic  importance :  the  Amphioxus,  the  lowest  Vertebrate 
form,  and  the  Ascidian,  the  most  neaiTy  allied  Invertebrate 
form,  have  both  descended  from  one  single  extinct  "Worm 
form,  which  must  have  possessed  the  essential  structure  of 
the  Chorda  Animals. 

The  Amphioxus,  as  has  already  been  often  shown,  is 
of  extreme  importance ;  not  only  because  it  thus  fills  the 
great  gap  between  the  Invertebrates  and  the  Vertebrates, 
but  also  because  it  represents,  at  the  present  time,  the 
typical  Vertebrate  in  its  simplest  form;  and  because  it 
directly  affords  the  best  standpoint  from  which  tc  examine 
the  gradual  historic  evolution  of  the  whole  tribe.  If  the 
structure   and   germ-history   of  the  Amphioxus   were  un- 


THE   AMPHIOXUS   AS   THE   ANCESTOR   OF   MAN.  99 

known  to  us,  the  whole  subject  of  the  development  of 
the  Vertebrate  tribe,  and  thus  of  our  own  race,  would  be 
enveloped  in  an  impenetrable  veil.  The  accurate  anatomical 
and  ontogenetic  knowledge  of  the  Amphioxus,  attained 
during  the  last  few  years,  has  alone  pierced  that  heavy  veil, 
formerly  supposed  to  be  impenetrable.  If  the  Amphioxus  is 
compared  with  the  developed  Man  or  any  other  of  the 
higher  Vertebrates,  a  great  number  of  striking  dissimilarities 
will  be  seen.  The  Amphioxus  has  no  specialized  head,  no 
brain,  no  skull,  no  jaws,  no  limbs  ;  it  is  without  a  central- 
ized heart,  a  developed  liver  and  kidneys,  a  jointed  vertebral 
column ;  every  organ  appears  in  a  much  simpler  and  more 
primitive  form  than  in  the  higher  Vertebrates  and  in  Man. 
(Cf.  Table  X.,  vol.  i.  p.  4GG.)  And  yet,  in  spite  of  all  these 
various  deviations  from  the  structure  of  other  Vertebrates, 
the  Amphioxus  is  a  genuine,  unmistakable  Vertebrate ; 
and  if,  instead  of  the  developed  Man,  the  human  embryo 
at  an  early  period  of  its  Ontogeny  is  compared  with 
the  Amphioxus,  we  shall  find  perfect  parallelism  between 
the  two  in  all  essential  points.  (Cf.  Table  IX.,  vol.  i.  p.  465.) 
This  highly  important  parallelism  justifies  the  conclusion 
that  all  the  Skulled  Animals  (Craniota)  have  descended 
from  a  common  primaeval  parent-form,  the  structure  of 
which  was  essentially  that  of  the  Amphioxus.  This  parent- 
form,  the  earliest  Primitive  Vertebrate,  possessed  the 
peculiar  characters  of  the  Vertebrates,  and  yet  was  without 
all  those  important  peculiarities  that  distinguish  the  Skulled 
Animals  from  the  Skull-less.  Although  the  Amphioxus  ap- 
pears peculiarly  organized  in  many  respects,  and  although 
it  may  not  be  regarded  as  an  unmodified  descendant  of  the 
Primitive  Vertebrate,  yet  it  must  have  inherited  from  the 


100  THE   EVOLUTION   OF   MAN. 

latter  the  distinguishing  characteristic  features  already 
mentioned.  We  cannot  therefore  say  that  the  Amphioxus  is 
the  progenitor  of  the  Vertebrates  ;  but  we  may  certainty  say 
that  the  Amphioxus  of  all  known  animals  is  nearest  allied 
to  this  progenitor ;  both  belong  to  the  same  limited  family 
group,  to  the  lowest  Vertebrate  class,  that  of  the  Skull-less 
Animals  (Acvania).  In  the  human  pedigree,  this  group 
forms  the  ninth  stage  of  the  ancestral  chain,  the  first  among 
Vertebrate  ancestors.  From  this  Skull-less  group  was 
developed  the  Amphioxus  on  the  one  side,  and  on  the  other 
the  parent-form  of  the  Skulled  Animals  (Craniota). 

The  comprehensive  group  of  the  Skulled  Animals 
includes  all  known  Vertebrates,  with  the  single  excep- 
tion of  the  Amphioxus.  All  these  Skulled  Animals 
possess  a  distinct  head,  inwardly  specialized  from  the 
trunk,  and  this  contains  a  skull,  enclosing  a  brain.  This 
head  also  carries  three  of  the  higher  sense-organs,  which  are 
partially  wanting  in  the  Skull-less  Animals  (nose,  ears,  and 
eyes).  At  first,  the  brain  appears  in  a  very  simple  form,  as 
an  anterior  bladder-like  extension  of  the  medullary  tube 
(Plate  XL  Fig.  16,  mj  This,  however,  is  soon  distributed  by 
several  tranverse  grooves — first  into  three,  and  afterwards 
into  a  series  of  five  consecutive  brain-bladders.  In  the 
formation  of  the  head,  skull,  and  brain,  together  with  the 
higher  sense-organs,  lies  the  most  essential  advance  made 
by  the  skulled  parent-form  beyond  its  skull-less  ancestors. 
Other  organs,  however,  also  soon  rose  to  a  higher  grade 
of  development ;  a  compact  centralized  heart  appeared,  a 
more  perfect  liver  and  kidneys;  and  in  other  directions 
also  important  advance  was  made. 

The   Skull-less  Animals  may  be  primarily  subdivided 


SKULL-LESS  ANIMALS.  10 1 

into  two  differing  main  sections,  that  of  the  Single-nostrils 
(Monorhina),  and  that  of  the  Double-nostrils  (Amphirhina). 
Of  the  former  there  are  but  very  few  extant  forms,  which 
are  called  Round-mouths  (Cyclostoma).  These  are,  however, 
of  great  interest,  because  in  their  whole  structure  they  are 
intermediate  between  the  Skull-less  Animals  and  the  Double- 
nostrils  (Amphirhina).  Their  organization  is  much  higher 
than  that  of  the  Skull-less  Animals,  much  lower  than  that 
of  the  Double-nostrils  ;  they  thus  form  a  very  welcome 
phylogenetic  link  between  those  two  divisions.  We  may 
therefore  represent  them  as  a  special,  tenth  stage  in  the 
human  ancestral  series. 

The  few  existing  species  of  the  class  of  Round-mouths  are 
distributed  into  two  different  orders,  which  are  distinguished 
as  the  Hags  and  the  Lampreys.  The  Hags  (Myxinoides) 
have  long,  cylindrical,  worm-like  bodies.  Linnreus  classed 
them  among  Worms,  but  later  zoologists  have  placed  them, 
sometimes  among  the  Fishes,  sometimes  Amphibians,  and 
a<min  with  Molluscs.  The  Hags  live  in  the  sea  and  are 
usually  parasitic  on  Fishes,  into  the  skin  of  which  they 
penetrate  by  means  of  their  round  sucking  mouths  and 
their  toothed  tongues.  They  are  occasionally  found  in  the 
body-cavity  of  Fishes — for  example,  of  the  Cod  and  Stur- 
geon— having  penetrated  to  the  interior  in  their  passage 
through  the  skin.  The  second  order,  that  of  the  Lampreys 
(Petromyzontes),  includes  those  well-known  "  Nine  eyes," 
common  at  the  seaside;  the  little  river  Lamprey  (Petro- 
myzon  flu  riot  His)  and  the  large  sea  Lamprey  (Petromyzon 
marinus,  Fig.  190). 

The  animals  included  in  the  two  groups  of  the  Myxi- 
noides and   the  Petromyzontes,  are   called    Round-mouths 


102  THE   EVOLUTION    OF   MAN. 

(Cyclostorna),  from  the  fact  that  their  mouth  forms  a  circular 
or  semi-circular  opening.  The  upper  and  under  jaws, 
which  appear  in  all  the  higher  Vertebrates,  are  completely 
wanting  in  the  Round-mouths,  as  in  the  Amphioxus.  All 
other  Vertebrates  are  therefore  distinguishable  from  them 
as  "Jaw-mouthed"  (Gnathostomi).  The  Round-mouths  may 
also  be  called  "  Single-nostrils  "  (Monorhina),  because  they 
have  but  a  single  nasal  tube,  while  the  Gnathostomi  are  all 
furnished  with  a  pair  of  nasal  cavities,  a  right  and  a  left 
nose-cavity  ("  Double-nostrilled,"  Amphirhhia).  But  in 
addition  to  these  peculiarities,  the  Jaw-mouths  are  also 
distinguished  by  many  other  remarkable  structural  arrange- 
ments, and  are  further  removed  from  the  Fishes  than  the 
latter  are  from  Man.  They  must,  therefore,  evidently  be 
regarded  as  the  last  remnant  of  a  very  old  and  very  low 
class  of  Vertebrates,  which  are  far  below  the  structural 
stage  of  a  genuine  Fish.  To  mention  here  briefly  only 
the  most  important,  the  Round-mouths  are  entirely  with- 
out any  trace  of  limbs.  Their  slimy  skin  is  quite 
naked  and  smooth,  without  scales.  They  are  wholly 
destitute  of  a  bony  skeleton.  The  inner  skeleton  axis  is 
a  very  simple  inarticulate  notochord,  like  that  of  the 
Amphioxus.  In  the  Lampreys  alone  a  rudimentary  articu- 
lation is  indicated  by  the  fact  that  upper  arches  appear  in 
the  vertebral  tube  proceeding  from  the  notochord  sheath. 
At  the  anterior  end  of  the  chorda  a  skull  is  developed  in 
its  very  simplest  form.  From  the  notochord  sheath  pro- 
ceeds a  small  soft-membraneous  skull  capsule,  which 
becomes  partly  cartilaginous :  this  capsule  encloses  the 
brain.  The  important  apparatus  of  the  gill-arches,  the 
tongue-bone,    etc.,  which    is    inherited   by    all  Vertebrates 


LAMPREYS. 


I03 


from  Fishes  to  Man,  is  wholly  wanting  in 
the  Round-mouths.  They  have,  indeed,  a 
superficial,  cartilaginous  gill-skeleton,  but  this 
is  of  quite  different  morphological  significance. 
On  the  other  hand,  in  them  we  meet,  for  the 
first  time,  with  a  brain,  that  important 
mental  organ,  which  has  been  transmitted 
from  the  Single-nostrils  up  to  Man.  It  is  time 
that  in  the  Round-mouths  the  brain  appears 
merely  as  a  very  small  and  comparatively 
insignificant  swelling  of  the  spinal  chord ;  at 
first  a  simple  bladder  (Plate  XL  Fig.  16,  mj, 
which  afterwards  separates  into  five  consecu- 
tive brain-bladders,  as  in  the  brains  of  all 
Double -breathers.  These  five  simple  primitive 
brain-bladders,  which  reappear  in  a  similar 
form  in  the  embryos  of  all  higher  Vertebrates, 
from  Fishes  up  to  Man,  and  which  undergo 
a  very  complex  modification,  remain  in  the 
Round-mouths,  in  a  very  low  and  undifferen- 
tiated stage  of  development.  The  histological 
elementary  structure  of  the  nervous  system  is 
also  much  more  imperfect  than  in  other  Verte- 
brates. While  in  the  latter  the  organ  of 
hearing  always  has  three  semi-circular  canals, 
in  the  Lampreys  it  has  but  two,  and  in  the 
Hags  but  one.  In  most  other  points  also, 
the    organization    of    the    Round-mouths    is 

Fig.  190. — The  largo  Sea-lamprey  (Petromyzon  mari- 
nus),  much  reduced  in  size.  A  series  of  seven  gill-open- 
ings are  visible  below  the  eye. 

28 


104  THE   EVOLUTION   OF  MAN. 

much  simpler  and  more  imperfect,  as,  for  instance,  in  the 
structure  of  the  heart,  the  circulatory  .system,  and  the 
kidneys.  In  them,  as  in  the  Amphioxus,  the  anterior 
portion  of  the  intestinal  canal  does,  indeed,  form  respiratory 
gills  ;  but  these  respiratory  organs  are  developed  in  a  very 
peculiar  way :  in  the  form  of  six  or  seven  little  pouches,  or 
sacs,  which  lie  on  both  sides  of  the  anterior  intestine  and 
communicate  with  the  throat  (pharynx)  by  inner  openings, 
and  by  outer  ones  with  the  external  skin.  This  is  a  very 
peculiar  formation  of  the  respiratory  organs,  quite  cha- 
racteristic of  this  class  of  animals.  They  have  therefore 
been  called  the  "  Pouch-gills "  (Marsu/pobrancliii).  The 
absence  of  one  very  important  organ  found  in  the  Fishes, 
the  swimming-bladder,  from  which  the  lungs  of  the  higher 
Vertebrates  have  developed,  should  be  especially  noticed. 

In  their  germ-history,  as  in  their  whole  anatomical  struc- 
ture, the  Round-mouths  present  many  peculiarities.  They 
are  even  peculiar  in  the  unequal  cleavage  of  the  egg,  which 
most  nearly  approaches  that  of  the  Amphibians  (Fig.  31, 
vol.  i.  p.  203).  This  results  in  the  formation  of  a  Hood- 
gastrula,  like  that  of  Amphibians  (Plate  II.  Fig.  11).  From 
this  develops  a  very  simple  organized  larval  form,  which  is 
closely  allied  to  the  Amphioxus,  and  which,  for  that  reason, 
we  examined  and  compared  with  the  latter  (vol.  i.  p.  428, 
and  Plate  VIII.  Fig.  16).  The  gradual  germ-evolution  of 
these  larva3  of  the  Round-mouths  explains  very  clearly  and 
unmistakably  the  gradual  evolution  of  the  Skulled  from  the 
Skull-less  class  of  Vertebrates.  At  a  later  period,  from 
this  simple  Lamprey  larva  is  developed  a  blind  and  tooth- 
less larval  form,  which  is  so  very  different  from  the  mature 
Lamprey  that,   until   twenty  years  ago,   it  was   generally 


ROUND-MOUTHS.  105 

described  as  a  peculiar  form  of  fish  under  the  name  of 
Ammoccetes.  By  a  further  metamorphosis  this  blind  and 
toothless  Ammoccetes  is  transformed  into  the  Lamprey  with 
eyes  and  teeth  (Petromyson).u1 

Summing  up  all  these  peculiarities  in  the  structure  and 
embryology  of  the  Round-mouths,  we  may  assert  that  the 
oldest  Skulled  Animals,  or  Craniota,  diverged  in  two  lines ; 
one  of  these  lines  has  continued  up  to  the  present  time 
but  little  modified;  it  is  represented  by  the  Cyclostoma, 
or  Monorhina,  forming  a  collateral  line  which  has  made 
but  little  progress,  but  has  remained  at  a  very  low  stage  of 
development.  The  other  line,  the  direct  line  in  the  pedigree 
of  the  Vertebrates,  advanced  in  a  straight  line  to  the  Fishes, 
and  by  new  adaptations  attained  many  important  improve- 
ments. 

In  order  rightly  to  appreciate  the  phylogenetic  signi- 
ficance of  interesting  remnants  of  primaeval  groups  of 
animals,  such  as  the  Round-mouths,  it  is  necessary  to  study 
minutely  their  various  peculiar  characters  philosophically 
and  with  the  aid  of  Comparative  Anatomy.  A  careful 
distinction  must  be  drawn  between  the  hereditary  cha- 
racters which  have  been  accurately  transmitted  to  the 
present  day  by  hei'edity  from  common,  primaeval  ancestors, 
now  extinct,  on  the  one  hand ;  and,  on  the  other,  those 
special  adaptive  peculiarities  which  the  existing  remnant 
of  that  primaeval  group  have,  in  the  course  of  time,  gained 
secondarily  by  adaptation.  To  the  latter  class  belong, 
for  example,  in  the  Round-mouths,  the  peculiar  formation 
of  the  single  nostril  and  the  round  sucking  mouth  ;  as 
well  as  special  structural  arrangements  of  the  epidermis 
and  the  pouch-shaped  gills.     But,  on  the  other  hand,  to  the 


106  THE   EVOLUTION   OF   MAN. 

former  class  of  characteristics,  which  alone  have  any  phylo- 
genetic  significance,  belong  the  primitive  formation  of  the 
vertebral  column  and  the  brain,  the  absence  of  the  swim- 
ming-bladder, of  jaws,  limbs,  etc. 

In  the  animal  system,  the  Round-mouths  are  usually 
classed  among  Fishes ;  but  that  this  is  quite  incorrect  is 
apparent  from  the  simple  fact  that,  in  all  important  and 
prominent  structural  peculiarities,  they  are  further  removed 
from  the  Fishes  than  the  Fishes  are  from  the  Mammals  and 
from  Man. 


CHAPTER  XVIII. 

THE   PEDIGREE   OF   MAN. 
III.  From  the  Primitive  Fish  to  the  Amniotic  Animal. 

Comparative  Anatomy  of  the  Vertebrates. — The  Characteristic  Qualities  of 
the  Double-nostrilled  and  Jaw-mouthed  :  the  Double-Nostrils,  the  Gill- 
arch  Apparatus,  with  the  Jaw-arches,  the  Swimming-bladder,  the  Two 
Pairs  of  Limbs. — Kelationship  of  the  Three  Groups  of  Fishes  :  the  Pri- 
mitive Fishes  (Selachii),  the  Ganoids  (Ganoides),  the  Osseous  Fishes 
(Teleostei). — Dawn  of  Terrestial  Life  on  the  Earth.— Modification  of 
the  Swimming-bladder  into  the  Lungs. — Intermediate  Position  of  the 
Dipncusta  between  the  Primitive  Fishes  and  Amphibia. — The  Three 
Extant  Dipneusta  (Protopterus,  Lepidosiren,  Ceratodus) . — Modification  of 
the  Many-toed  Fin  of  the  Fish  into  the  Five-toed  Foot. — Causes  and 
Effects  of  the  latter. — Descent  of  all  Higher  Vertebrates  from  a  Five-toed 
Amphibian. — Intermediate  Position  of  the  Amphibians  between  the 
Lower  and  Higher  Vertebrates. — Modification  or  Metamorphosis  of 
Frogs. — Different  Stages  in  Amphibian  Metamorphosis. — The  Gilled 
Batrachians  (Proteus  and  Axolotl). — The  Tailed  Batrachians  (Salaman- 
ders and  Mud-fish). — Frog  Batrachians  (Frogs  and  Toads). — Chief 
Group  of  the  Amnion  Animals,  or  Amniota  (Reptiles,  Birds,  and 
Mammals). — Descent  of  all  the  Amniota  from  a  Common  Lizard-like 
Parent-form  (Protamnion) . — First  Formation  of  the  Allantois  and  of  the 
Amnion. — Branching  of  the  Amnion  Animals  in  Two  Lines  :  on  the  one 
side,  Reptiles  (and  Birds),  on  the  other  side,  Mammals. 

"  The  imagination  is  an  indispensable  faculty ;  for  it  is  that  which,  by 
forming  new  combinations,  occasions  important  discoveries.  The  naturalist 
needs  both  the  discriminating  power  of  abstract  reason,  and  the  generalizing 
power  of  the  imagination,  and  that  the  two  should  be  harmoniously  inter. 


IOS  THE   EVOLUTION   OF  MAN. 

related.  If  the  proper  balance  of  these  faculties  is  destroyed,  the  naturalist 
is  hurried  into  chimerical  fancies  by  his  imagination ;  while  the  same  gift 
leads  the  gifted  naturalist  of  sufficient  strength  of  reason  to  the  most 
important  discoveries." — Johannes  Mulleb.  (1834). 

The  further  we  proceed  in  human  tribal  history,  the  nar- 
rower does  that  part  of  the  animal  kingdom  become  within 
which  we  must  look  for  extinct  ancestors  of  the  human 
race.  At  the  same  time,  the  evidence  as  to  the  history  of 
the  evolution  of  our  race  given  by  what  we  have  called  the 
records  of  creation,  the  evidence  of  Ontogeny,  of  Compara- 
tive Anatomy,  and  of  Palaeontology,  grows  constantly  more 
extensive,  complete,  and  trustworthy.  It  is  therefore 
natural  that  Phylogeny  should  assume  a  more  definite  form 
the  nearer  we  approach  the  higher  and  the  highest  stages 
of  the  animal  kingdom. 

Comparative  Anatomy  especially  has  done  far  more  for 
our  knowledge  of  these  higher  stages  of  evolution  in  the 
animal  kingdom  than  for  the  lower.  This  important 
science,  which  aims  at  a  true  philosophy  of  organic  forms, 
has  made  greater  progress  in  the  Vertebrate  tribe  than  in  any 
section  of  the  Invertebrate.  Cuvier,  Meckel,  and  Johannes 
Miiller  had  already  laid  a  deep  and  extensive  foundation ; 
and  now  the  Comparative  Anatomy  of  Vertebrates  has 
recently  been  powerfully  advanced  by  the  admirable  inves- 
tigations of  Owen  and  Huxley,  and,  especially,  has  been 
perfected  to  such  a  degree  by  the  unsurpassed  labours  of 
Gegenbaur,  that  it  now  forms  one  of  the  strongest  supports 
of  the  Theory  of  Descent.  Relying  on  the  evidence  thus 
furnished,  we  can  now,  with  a  great  degree  of  certainty, 
recognize  the  most  important  outlines  of  the  series  of  stages 
and  the  ramifications  of  the  Vertebrate  pedigree. 


PEIMITIVE   FISHES.  IO9 

That  part  of  the  animal  kingdom  with  which  we  are 
now  concerned  has  become  so  narrow,  even  before  we  have 
left  the  Archilithic  Epoch,  that  but  a  single  one  of  the 
seven  tribes  of  the  animal  kingdom  forms  the  object  of  our 
study.  Even  within  this  tribe  we  have  passed  the  lowest 
steps,  and  have  risen  above  the  Skull-less  (Acrania)  and 
Double-nostrilled  Vertebrates  (Monorhina),  to  the  class  of 
Fishes.  The  latter  are  the  first  of  the  great  main  division 
of  Vertebrates  distinguished  by  mouths  with  jaws  and  by 
double  nostrils  (Amphirhina,  or  Gnathostoma).  From  Fishes 
we  start  again,  as  from  that  class  of  Vertebrates  which  are 
indubitably  shown  by  Comparative  Anatomy  and  Ontogeny 
to  be  the  ancestral  class  of  all  higher  Vertebrates,  all  Am- 
phirhina. Of  course  no  existing  Fish  can  be  regarded  as 
the  direct  parent-form  of  the  higher  Vertebrates.  But  it  is 
ecpially  certain  that  from  a  common  extinct  Fish-like 
parent-form  we  may  trace  all  those  Vertebrates  from  Fishes 
up  to  Man,  which  are  included  under  the  name  of  Am- 
phirhina. If  this  primaeval  parent-form  were  extant,  we 
should  undoubtedly  describe  it  as  a  genuine  Fish  and  class 
it  among  Fishes.  Fortunately,  the  Comparative  Anatomy 
and  Classification  of  the  Fishes  has  been  so  far  advanced 
(thanks  to  the  labours  of  Johannes  Miiller  and  Gegenbaur) 
that  we  can  very  clearly  distinguish  these  most  important 
and  interesting  genealogical  relations. 

In  order  correctly  to  understand  the  human  pedigree 
within  the  Vertebrate  tribe,  it  is  very  important  to  bear  in 
mind  the  distinguishing  characteristics,  separating  Fishes 
and  all  the  other  Double-nostrils  (Amphirhina)  from 
Single-nostrilled  and  Skull-less  Animals  (Monorhina  and 
Acrania).     These  very  distinguishing  characteristic  marks 


HO  THE   EVOLUTION   OF   MAN. 

Fishes  have  in  common  with  all  other  Double-nostrils  up 
to  Man,  and  it  is  on  this  parallelism  that  we  found  our 
claim  of  relationship  to  Fishes.  (Cf.  Table  X.,  vol.  i. 
p.  466.)  The  following  characters  of  the  Double-nostrils 
must  be  especially  indicated  as  the  systematic  anatomical 
features  of  the  highest  importance :  (1)  the  double  structure 
of  the  nose;  (2)  the  internal  gill-arch  apparatus,  together 
with  the  jaw-arches ;  (3)  the  swimming-bladder,  or  lungs  ; 
and  (4)  the  two  pairs  of  limbs. 

As  to  the  nasal  structure,  on  which  is  based  the  distinc- 
tion of  the  Single-nostrils  {Monorhina)  from  the  Double- 
nostrils  (Amphirhina),  it  is  certainly  significant  that  even  in 
Fishes  the  earliest  rudiment  of  the  nose  consists  of  two  en- 
tirely distinct  lateral  grooves  or  pits  in  the  outer  surface  of 
the  head,  just  as  is  the  case  in  the  embryo  of  Man  and  of  all 
higher  Vertebrates.  On  the  other  hand,  in  Single-nostrils 
and  Skull-less  Vertebrates  the  first  rudiment  of  the  nose  is, 
from  the  first,  a  single  pit  in  the  centre  of  the  forehead 
region.  No  less  important  is  the  higher  development  of  the 
skeleton  of  the  gill-arch  and  of  the  jaw  apparatus  connected 
with  it,  as  it  occurs  in  all  Double-nostrils  from  Fishes  to 
Man.  It  is  true  that  the  primitive  modification  of  the 
anterior  intestine  into  the  gill-intestine,  which  occurs  even 
in  Ascidians,  is  developed  in  all  Vertebrates  from  one  simple 
rudiment;  and  in  this  respect  the  gill-openings,  which  in 
all  Vertebrates  and  also  in  Ascidians  pierce  the  wall  of  the 
gill-intestine,  are  quite  characteristic.  But  the  external 
framework  of  the  gills,  which  in  all  Skull-less  and  Single- 
nostrilled  Animals  (Acraniota  and  Monorhina)  supports 
the  gill-body,  is  displaced  in  all  Double-nostrils  (Amphi- 
rhina)  by  an  internal  gill-skeleton  which  replaces  the  former. 


DOUBLE-NOSTRILS  AND   SINGLE-NOSTRILS.  Ill 

This  internal  gill-support  consists  of  a  consecutive  series  of 
cartilaginous  arches,  which  are  situated  between  the  gill- 
openings  within  the  wall  of  the  throat  (pharynx),  and 
extend  round  the  throat.  The  foremost  of  these  pairs  of 
gill-arches  changes  into  the  jaw-arch  (maxillary  arch), 
which  gives  rise  to  the  upper  and  lower  jaws. 

A  third  essential  character  by  which  all  Double-nostrils 
are  well  distinguished  from  all  those  lower  Vertebrates 
which  we  have  already  considered,  is  the  formation  of  a 
blind  sac  which  protrudes  from  the  anterior  portion  of  the 
intestinal  canal,  and  which  in  the  Fishes  becomes  the  air- 
filled  swimming-bladder  (Plate  V.  Fig.  13,  hi).  As  this 
organ,  in  proportion  as  it  contains  a  greater  or  less  quantity 
of  air,  or  in  proportion  as  this  air  is  more  or  less  compressed, 
imparts  a  higher  or  lower  specific  gravity  to  the  Fish,  it 
acts  as  a  hydrostatic  apparatus.  By  this  means  the  Fish 
can  rise  or  sink  in  the  water.  This  swimming-bladder  is 
the  organ  from  which  the  lung  of  higher  Vertebrates  has 
developed.  The  fourth  and  last  main  character  of  Double- 
nostrils  is  the  presence  of  two  pairs  of  extremities  or 
members  in  the  primitive  arrangement  of  the  embryo ;  a 
pair  of  fore  limbs,  which  in  Fishes  are  called  pectoral  fins 
(Fig.  191,  v),  and  a  pair  of  hind  limbs,  which  in  Fishes  are 
called  ventral  fins  (Fig.  191,  h).  The  Comparative  Anatomy 
of  these  fins  is  of  supreme  interest,  because  they  contain 
the  rudiments  of  all  those  parts  of  the  skeleton  which,  in 
all  the  higher  Vertebrates  up  to  Man,  form  the  skeleton  or 
support  of  the  extremities  of  the  fore  and  hind  limbs.  In 
Skull-less  and  Single-nostrilled  Animals  there  is,  on  the 
contrary,  no  trace  of  these  extremities.  In  addition  to 
these  four  most  important  main  characters  of  the  Amphi- 


112  THE   EVOLUTION   OF   MAN. 

rhina,  we  might  further  mention  the  presence  of  a  sym- 
pathetic nerve-system,  a  spleen,  a  ventral  salivary  gland  ; 
organs  which  are  not  represented  in  the  lower  Vertebrates 
already  considered.  All  these  important  parts  have  trans- 
mitted themselves  from  Fishes  up  to  Man,  and  from  this 
circumstance  alone  it  is  evident  how  wide  a  chasm  sepa- 
rates the  Fishes  from  the  Skull-less  and  Single-nostrilled 
Animals  (Acraniota  and  Monorhina).  Fishes  and  Man 
possess  all  these  characters  in  common  (Table  X.). 

Turning  now  to  consider  the  Fish  class  in  greater  detail, 
we  may  divide  it  primarily  into  three  main  groups,  or  sub- 
classes, the  genealogies  of  which  are  evident.  The  first 
and  most  ancient  group  is  that  of  the  Primitive  Fishes 
(Selachii),  the  best-known  extant  representatives  of  which 
are  the  members  of  the  much-varied  orders  of  Sharks  and 
Rays  (Figs.  191,  192).  These  are  followed  by  a  series  of 
further  developed  Fish  forms,  by  the  sub-class  of  Mucous 
Fishes  (Ganoides).  The  greater  number  of  these  have  long 
been  extinct,  and  only  very  few  living  representatives  are 
known  ;  these  are  the  Sturgeon  and  Huso  of  European  seas, 
the  Polypterus  of  African,  and  the  Lepidosteus  and  Amia 
of  American  rivers.  The  earlier  abundance  of  forms  belong- 
ing to  this  interesting  group  is,  however,  proved  by  the 
abundance  of  their  fossil  remains.  From  these  Mucous 
Fishes  originated  the  third  sub-class,  that  of  the  Osseous 
Fishes  (Teleostei),  to  which  belong  most  extant  Fishes,  espe- 
cially nearly  all  our  river  fish.  Comparative  Anatomy 
and  Ontogeny  very  clearly  show  that  the  Ganoids  sprang 
from  the  Selachii,  just  as  the  Teleostei  sprang  from  the 
Ganoids.  But,  on  the  other  hand,  a  second  side-line,  or 
rather   the  main  ascending  line    of  the    Vertebrate  tribe, 


EMBRYOS   OF   SHARKS 


Fig.  191. 


Fig.  192. 


114  THE   EVOLUTION   OF  MAN. 

Fig.  191. — Embryo  of  a  Shark  (Scymnus  lichia),  seen  from  ventral  side  : 
v,  pectoral  fins  (in  front  of  these  five  pairs  of  gill-openings)  ;  h,  ventral  fins  ; 
a,  anal  opening  ;  s,  tail  fin  ;  k,  external  gill-tufts  ;  d,  yelk-sac  (the  greater 
part  of  this  has  been  removed)  ;  g,  eye  ;  n,  nose ;  m,  mouth  fissure. 

Fig.  192. — Developed  Man-shark  (Carcharias  melanopterus),  seen  from 
the  left  side  :  r1  first,  r2  second  dorsal  fin;  s,  tail  fin;  a,  anal  fin;  v,  pectoral 
fins  ;  7i,  ventral  fins. 

developed  in  another  direction  from  the  Primitive  Fishes; 
this  line  leads  upward  through  the  Dipneusta  group  to  the 
important  class  of  Amphibia. 

This  significant  relationship  between  the  three  groups 
of  Fishes  has  been  placed  beyond  all  doubt  by  the  re- 
searches of  Gegenbaur  on  the  subject.  The  lucid  discussion 
on  the  "  systematic  position  of  the  Selachii "  which  that 
author  inserted  in  the  introduction  to  his  classic  study  of 
the  "head  skeleton  of  the  Selachii,"  must  be  regarded  as 
definitely  proving  this  important  relation.148  In  Primitive 
Fishes  (Selachii),  however,  the  scales  (skin  appendages) 
and  the  teeth  (jaw  appendages)  are  identical  in  formation 
and  structure,  while  in  the  other  two  groups  of  Fishes 
(Mucous  and  Osseous  Fishes)  these  organs  have  already 
become  distinct  and  differentiated.  Moreover,  in  Primitive 
Fishes,  the  cartilaginous  skeleton  (the  vertebral  column 
and  the  skull,  as  well  as  the  members)  is  of  the  simplest 
and  most  primitive  nature,  of  which  the  bony  skeletons 
of  Mucous  and  Osseous  Fishes  must  be  regarded  as  a 
modification.  It  is  true  that  in  certain  respects  (in  the 
structure  of  the  heart  and  of  the  intestinal  canal)  Mucous 
Fishes  fully  coincide  with  Primitive  Fishes,  and  differ  from 
Osseous  Fishes.  But  a  comparative  review  of  all  the 
anatomical  relations  plainly  shows  that  the  Mucous  Fishes 
constitute    a    connecting    group    between    Primitive    and 


MUD-FISHES.  1 1 5 

Osseous  Fishes.  The  Primitive  Fishes  (Selachii)  form  the 
most  ancient  and  original  group  of  Fishes.  From  these, 
in  one  direction,  all  other  Fishes  have  developed ;  the 
Mucous  Fishes  first,  which,  at  a  much  later  period  (in  the 
Jurassic,  or  the  Chalk  Period),  gave  rise  to  the  Osseous 
Fishes.  In  another  direction,  the  Primitive  Fishes  gave 
rise  to  the  parent-forms  of  the  higher  Vertebrates,  directly 
to  the  Dipneusta,  and  thus  to  Amphibians.  Regarding  the 
Selachii  as  forming  the  eleventh  stage  in  our  pedigree,  these 
would  be  followed  by  the  Dipneusta  group  as  the  twelfth 
stage,  and  by  the  Amphibian  group  as  the  thirteenth  stage. 
The  advance  effected  in  the  development  of  the  Mud- 
fishes (Dipneusta)  from  the  Primitive  Fishes  is  of  great  mo- 
ment, and  is  connected  with  a  very  noticeable  change,  which 
took  place  in  the  beginning  of  the  Palaeozoic,  or  Primary 
Period  in  organic  life  as  a  whole.  For  the  very  numerous 
fossil  remains  of  plants  and  animals  which  are  now  known  to 
belong  to  the  first  three  epochs  of  the  history  of  the  earth — 
to  the  Laurentian,  the  Cambrian,  and  the  Silurian  Periods, 
are  exclusively  those  of  aquatic  plants  and  animals.  From 
this  palreontological  fact,  taken  in  connection  with  certain 
weighty  geological  and  biological  considerations,  we  may 
infer,  with  tolerable  certainty,  that  at  that  time  no  land 
animals  yet  existed.  During  the  whole  of  the  enormous 
Archizoic  Period — during  many  millions  of  years — the  living 
population  of  our  globe  were  all  water-dwellers :  a  very 
remarkable  fact,  when  it  is  remembered  that  this  period 
embraces  the  larger  half  of  the  entire  organic  history  of  the 
earth.  The  lower  animal  tribes  are  even  now  exclusively, 
or  with  very  few  exceptions,  aquatic.  But  during  the 
Archizoic,  or  Primordial  Epoch,  the  higher  animal  tribes 


Il6  THE   EVOLUTION   OF   MAN. 

continued  exclusively  adapted  to  aquatic  habits  of  life.  It 
was  not  till  later  that  they  adopted  a  land  life.  The  earliest 
fossils  of  terrestrial  animals  occur  in  the  Devonian  strata, 
which  were  deposited  in  the  beginning  of  the  second  great 
division  of  the  earth's  history  (the  Palaeozoic  Epoch).  They 
increase  greatly  in  number  in  the  deposits  of  the  Coal  and 
Permian  Periods.  Even  in  these  early  formations  many 
terrestrial  and  air-breathing  species,  both  of  the  Arthro- 
pod and  of  the  Vertebrate  tribe,  occur ;  while  their  aquatic 
ancestors  of  the  Silurian  Period  breathed  nothing  but 
water.  This  physiologically  significant  modification  of  the 
mode  of  respiration  is  the  most  influential  change  that 
affected  the  animal  organism  in  the  transition  from  water 
to  dry  land.  In  the  first  place  it  caused  the  development 
of  an  air-breathing  organ,  the  lung,  the  water-breathing 
gills  having  previously  acted  as  respiratory  organs.  Simul- 
taneously, however,  it  effected  a  remarkable  change  in  the 
circulation  of  the  blood  and  in  the  organs  connected  with 
this ;  for  these  are  always  most  closely  correlated  with  the 
respiratory  organs.  In  addition  to  these,  other  organs  also, 
either  in  consequence  of  more  remote  correlation  with  the 
respiratory  organs,  or  in  consequence  of  new  adaptations, 
were  more  or  less  modified. 

Within  the  Vertebrate  tribe  it  was  undoubtedly  a  branch 
of  the  Primitive  Fishes  (Selachii)  which,  during  the  De- 
vonian Period,  made  the  first  successful  effort  to  accustom 
itself  to  terrestrial  life  and  to  breathe  atmospheric  air.  In 
this  the  swimming-bladder  was  especially  of  service,  for  it 
succeeded  in  adapting  itself  to  respiration  of  air,  and  so 
became  a  lung.  The  immediate  consequence  of  this  was 
the  modification  of  the  heart  and  nose.     While  true  Fishes 


EVOLUTION   OF   MUD-FISHES.  117 

have  only  two  blind  nose-pits  on  the  surface  of  the  head, 
these  now  became  connected  with  the  mouth-cavity  by  an 
open  passage.  A  canal  formed  on  each  side,  leading  directly 
from  the  nose-pit  into  the  mouth-cavity,  and  thus  even 
while  the  mouth-opening  was  closed  the  necessary  atmo- 
spheric air  could  be  introduced  into  the  lungs.  While, 
moreover,  in  all  true  Fishes  the  heart  consists  simply  of  two 
compartments,  an  auricle,  which  receives  the  venous  blood 
from  the  veins  of  the  body,  and  a  ventricle,  which  forces 
this  blood  through  an  arterial  expansion  into  the  gills,  the 
auricle,  owing  to  the  formation  of  an  incomplete  partition 
wall,  is  now  divided  into  a  right  and  a  left  half. 
The  right  auricle  alone  now  received  the  venous  blood  of 
the  body,  while  the  left  auricle  received  the  pulmonic 
venous  blood  passing  from  the  lungs  and  the  gills  to  the 
heart.  The  simple  blood-circulation  of  the  true  Fishes  thus 
became  the  so-called  double  circulation  of  the  higher  Ver- 
tebrates ;  and  this  development  resulted,  in  accordance  with 
the  laws  of  correlation,  in  further  progress  in  the  structure 
of  other  organs. 

The  vertebrate  class,  which  thus  first  adapted  itself  to 
the  habit  of  breathing  air,  and  which  originated  from  a 
branch  of  the  Selachii,  are  called  Mud-fishes  (Dijmeusta), 
or  Double-breathers,  because,  like  the  lowest  Amphibia, 
they  retain  the  earlier  mode  of  breathing  through  the  gills, 
in  addition  to  the  newly  acquired  lung-respiration.  This 
class  must  have  been  represented  by  numerous  and  diverse 
genera  during  the  Palaeolithic  Epoch  (during  the  Devonian, 
Carboniferous,  and  Permian  Periods).  As,  however,  the 
skeleton  is  soft  and  cartilaginous,  like  that  of  the  Selachii, 
they  naturally  left  no  fossil  remains.     The  hard  teeth  of 


1 18  THE   EVOLUTION   OF  MAN. 

single  genera  (Ceratodus)  could  alone  endure ;  these  occur, 
for  instance,  in  the  Trias.  At  the  present  time  there  are 
only  three  extant  genera  of  this  whole  class :  Protoptevus 
annectens,  in  the  rivers  of  tropical  Africa  (White  Nile, 
Niger,  Quillimane,  etc.) ;  Lepidosiren  pavadoxa,  in  tropical 
South  America  (in  the  tributaries  of  the  Amazon) ;  and 
Ceratodus  Fosteri,  in  the  swamps  of  Southern  Australia 
(Plate  XII.).149  This  wide  distribution  of  the  three  isolated 
descendants  of  the  class  is  alone  sufficient  to  prove  that 
they  are  the  last  remnants  of  a  group  which  was  formerly 
very  widely  developed.  The  whole  structure  of  their 
bodies  shows  that  the  group  to  which  they  belong  forms  the 
transition  between  Fishes  and  Amphibia.  The  direct  tran- 
sitional structure  between  the  two  classes  is  so  clearly 
expressed  in  the  whole  organization  of  these  curious  animals, 
that  zoologists  yet  dispute  whether  the  Dipneusta  are 
Fishes  or  Amphibia.  Some  well-known  zoologists  still  class 
them  among  Amphibia,  while  they  are  usually  placed 
among  Fishes.  In  fact,  the  characters  of  both  the  classes 
are  so  united  in  the  Dipneusta  that  the  answer  to  the 
question  as  to  their  nature  depends  entirely  upon  the  mean- 
ing attached  to  the  terms  "  Fish  "  and  "  Amphibian."  In 
their  mode  of  life  they  are  true  Amphibia.  During  the 
tropical  winter,  in  the  rainy  season,  they  swim  in  the  water 
like  Fishes  and  inhale  water  through  the  gills.  During  the 
dry  season  they  burrow  in  the  mud  as  it  dries  up,  and 
during  that  period  breathe  air  through  lungs,  like  Am- 
phibians and  higher  Vertebrates.  In  this  two-fold  respira- 
tion they  do,  it  is  true,  coincide  with  the  lower  Amphibia, 
and  stand  far  above  Fishes.  Yet,  in  most  other  characters 
they  more  nearly  resemble  the  latter,  and  stand  below  the 


EXTANT   MUD-FISHES.  1 1 9 

former.  Their  external  appearance  is  entirely  like  that  of 
Fishes. 

The  head  of  the  Dipneusta  is  not  distinct  from  the 
trunk.  The  skin  is  covered  with  large  fish-scales.  The 
skeleton  is  soft,  cartilaginous ;  its  development  has  been 
arrested  at  a  very  low  stage,  just  as  in  the  lower  Primitive 
Fishes.  The  notochord  is  retained  entire.  The  two  pairs  of 
limbs  are  very  simple  fins  of  primitive  structure,  like  those 
of  the  lowest  Primitive  Fishes.  The  structure  of  the  brain, 
of  the  intestinal  tube,  and  the  sexual  organs,  is  also  as  in 
Primitive  Fishes.  The  Dipneusta,  or  Mud-fishes,  have,  there- 
fore, by  heredity,  accurately  retained  many  features  of  a 
lower  organization  derived  from  our  primosval  Fish  ancestors, 
while  their  adoption  of  the  habit  of  breathing  air  through 
lungs  introduced  a  great  advance  in  the  vertebrate  organi- 
zation. 

Moreover,  the  three  extant  Mud-fishes  differ  a  good  deal 
from  one  another  in  important  points  of  structure.  The 
Australian  Mud-fish  {Ceratodus),  which  was  first  described 
at  Sidney  in  1870  by  Gerard  Krefft,  and  which  attains  a 
length  of  six  feet,  appears  in  an  especial  degree  to  represent 
a  primaeval  and  very  conservative  animal  form  (Plate  XII.). 
This  is  especially  true  of  the  structure  of  its  simple  lung, 
and  of  its  fins,  which  contain  a  pinnate  skeleton.  In  the 
African  Mud-fish  {Protopterus),  on  the  contrary,  and  in  the 
American  form  (Lepidosiren)  the  double  lung  is  present,  as 
in  all  higher  Vertebrates ;  nor  is  the  fin-skeleton  pinnate. 
In  addition  to  the  internal  gills,  Protopterus  has  also  ex- 
ternal gills,  which  are  wanting  in  Lepidosiren.  Those 
unknown  Dipneusta,  which  were  among  our  direct  ancestors, 
and  which  formed  the  connecting  link  between  the  Selachii 


(       120      ) 

TABLE    XX. 

Systematic  Survey  of  the  Thylo  genetic  Classification  of 
Vertebrates. 


I.  <SfcuIl=Icss  (Acrania),  or  2Tubc4jrartcti  (Leptocardia). 
Vertebrates  without  a  specialized  head,  skull,  brain,  or  centralized  heart. 


1.  SiutlWrss 
Acrania 


I.  Tube-hearted 
Leptocardia 


1.  Lancelets 


1.  Amphioxida 


II.  Animals  nritrj  skulls  (Craniota)  and  with  centralist!  fjrarts  (Pachycardia). 

Vertebrates  with  specialized  head,  vrith  skull  and  brain,  and  with  a 

centralized  heart. 


Main-classes 

of  the 

SJculle'd  Animals. 


Classes 

of  the 

Skulled  Animals. 


Sub-classes 

of  the 

Skulled  Animals. 


Systematic  Xame 

of  the 

Sub-classes. 


2.  Single* 

flostrillrti 
Monorhina 


3.   Xon* 
amnionatc 
Anamnia 


Animals 
Amniota 


II.  Eound  mouths 
Cyclostoma 

III.  Fishes 
Pisces 

IV.  Mud-fishes 
<          Dipneusta 

V.  Batrachians 

Amphibia 


VI.  Reptiles 

Eeptilia 


VII.  Birds 

Aves 


VIII.  Mammals 

Mammalia 


2.  Hags,  or 

Mucous  Fish 

3.  Lampreys 

4.  Primitive  Fish 

5.  Ganoid  Fish 

6.  Osseous  Fish 

I   7.  Single-lunged 
{  8.  Double-lunged 
r  9.  Mailed    Batra- 
chians 
10.  Naked     Batra- 
[  chians 

/ll.  Lizards 

12.  Snakes 

13.  Crocodiles 

1 14.  Tortoises 

1 15.  Sea. dragons 

1 16.  Dragons 

17.  Flying  Reptiles 
l18.  BeakedAnimals 

119.  Long-tailed 
20.  Fan-tailed 
21.  Bush-tailed 
122.  CloacalAnimals 
23.  Pouched     Ani- 
mals 
24.  Placental    Ani- 
mals 


2.  Hyperotreta 
(Myxinoida) 

3.  Hyperoartia 
(Petromyzontia) 

4.  Selachii 

5.  Ganoides 

6.  Teleostei 

7.Monopneumones 

8.  Dipneumones 

9.  Phractamphibia 

10.  Lissamphibia 

11.  Lacertilia 

12.  Ophidia 

13.  Crocodilia 

14.  Chelonia 

15.  Halisauria 

16.  Dinosauria 

17.  Pterosauria 

18.  Anomodonta 

19.  Saururae 

20.  Carinatoe 

21.  Ratitge 

22.  Monotrema 

23.  Marsupialia 

24.  Placentalia 


(       121       ) 


TABLE   XXL 

Pedigree  of  Vertebrates.     {Of.  Plate  XV.) 


Osseous  fish 

Teleostei 


Ganoid  fish 
Ganoides 


Single-lunged 
Monopnenmones 


Double-lunged 
Dipneumones 


8.  ftlammals 
Mammalia 


7.  Birds 
Aves 

I 
6.  Eeptiles 

Reptilia 


Mud-fish 
Protopteri 


2tmmon=l3ntntaIs 

Amniota 
I 

5.  Batrachtans 
Amphibia 


4.  fHutefisfj 

Lipneusta 


Primitive  fisbes     Selachii 
.3.  Fisbes     Pisces 
Doublr=nostrilUJ 
Ampbirhina 


Lampreys  Hags 

Petromyzontes  Myxinoides 


2.  Round-mouths 

Cylostoma 


Sea-squirts 
AscidiiB 


Sea-barrels 
Thaliacea 


iHantlrtJ  Quintals 
Tunicata 


S>inrjIr=nostrtllrtJ    Monorhina 

£iuillrti=Hnimals    Craniota 


1.  Tube-hearted 
Leptocardia 


£IutU4rss 

Acrania 

Uertcbratrs 
Vertebrata 


dfjortia^nmials 
Chordonia 


WormB 
Vermes 


122  THE   EVOLUTION   OF  MAN. 

and  the  Amphibians,  were  doubtless  in  many  respects 
different  from  their  three  direct  descendants  of  the  present 
time,  but  in  the  most  essential  characters  they  must  have 
coincided  with  the  latter.  Unfortunately,  the  germ-history 
of  the  three  surviving  Mud-fishes  is  as  yet  entirely  un- 
known; probably  at  some  future  time  it  will  afford  us 
further  important  information  as  to  the  tribal  history  of  the 
lower  Vertebrates  and  so  of  our  ancestors. 

Very  important  information  of  this  kind  has  been 
supplied  by  the  next  Vertebrate  class,  that  of  the  Batra- 
chians  (Amphibia),  which  is  directly  connected  with  the 
Dipneusta,  from  which  it  originated.  To  this  class  belong 
the  Axolotl,  Salamanders  (Plate  XIII.),  Toads,  and  Frogs. 
Formerly,  after  the  example  of  Linnaeus,  all  Reptiles  (Lizards, 
Snakes,  Crocodiles,  and  Tortoises)  were  also  classed  among 
Amphibia.  But  these  animals  are  of  a  far  higher  organiza- 
tion, and  in  the  most  important  characters  of  their  ana- 
tomical structure  are  more  nearly  allied  to  Birds  than  to 
Amphibians.  The  true  Amphibia,  on  the  other  hand,  are 
more  nearly  allied  to  the  Double-breathers  and  to  Primitive 
Fishes  :  they  are  also  much  older  than  Reptiles.  Even  as 
earl}7  as  the  Carboniferous  Period  numerous  very  highly 
developed  Amphibia  (some  of  large  size)  were  extant,  whereas 
the  earliest  Reptiles  first  appear  only  towards  the  close  of 
the  Permian  Period.  In  all  probability  the  Amphibia  were 
developed  from  Double-breathers  at  an  even  earlier  period — 
during  the  Devonian  Period.  The  extinct  Amphibia,  of 
which  fossil  remains  have  been  preserved  from  that  most 
ancient  Primaeval  Epoch — and  these  are  especially  numerous 
in  the  Trias — were  distinguished  by  a  large  bony  coat  of  mail 
overlying  the  skin  (like  that  of  the  Crocodile),  while  most 


BATRACHIANS.  123 

of  the  yet  extant  Amphibians  have  a  smooth  and  slippery 
skin.  The  latter,  also,  are  on  an  average  smoother  than  the 
former,  and  must  be  regarded  as  their  stunted  posterity. 

Among  the  Amphibia  of  the  present  time  we  are, 
therefore,  unable  to  find  any  forms  that  are  directly  referable 
to  the  pedigree  of  the  human  race,  or  that  are  to  be  re- 
garded as  ancestors  of  the  three  higher  Vertebrate  classes  ; 
yet,  in  important  points  of  their  internal  anatomical  struc- 
ture, and  especially  in  their  germ-development,  they  cor- 
respond so  closely  with  us,  that  we  are  justified  in  affirming 
that  between  the  Double-breathers  (Dlpneusta)  on  the  one 
hand,  and  the  three  higher  Vertebrate  classes  (grouped 
together  as  Amniota)  on  the  other,  there  existed  a  series  of 
extinct  intermediate  forms  which,  if  we  had  them  before  us, 
we  should  class  among  Amphibia.  The  whole  organization 
of  the  extant  Amphibia  represents  a  transitional  group  of 
this  kind.  In  the  important  matters  of  respiration  and 
circulation  of  the  blood,  they  are  still  closely  allied  to  the 
Double-breathers,  although  in  other  respects  they  rise  above 
the  latter  This  is  especially  true  with  respect  to  the  ad- 
vanced structure  of  their  limbs  or  extremities.  The  latter 
here  for  the  first  time  appear  as  feet  with  five  digits.  The 
thorough  researches  of  Gegenbaur  have  shown  that  the  fins 
of  Fishes,  concerning  which  very  erroneous  views  were  pre- 
viously held,  are  feet  with  numerous  digits ;  that  is  to  say, 
the  several  cartilaginous  or  osseous  rays,  many  of  which  occur 
in  every  Fish-fin,  correspond  to  the  fingers  or  digits  on  the 
limbs  of  higher  Vertebrates.  The  several  joints  of  each  ray 
correspond  to  the  several  joints  of  each  digit.  In  the  Double- 
breathers  the  fin  yet  retains  the  same  structure  as  in  Fishes, 
and  it  was  only  gradually  that  the  five-toed  form  of  foot, 


124  THE   EVOLUTION   OF  MAN. 

which  occurs  for  the  first  time  in  Amphibians,  was  developed 
from  this  multi-digitate  form.  This  reduction  in  the  number 
of  the  digits  from  ten  to  five  occurred  in  those  Dipneusta 
which  must  be  regarded  as  the  parent-forms  of  the  Amphibia, 
probably  as  early  as  the  latter  half  of  the  Devonian  Period — 
or,  at  latest,  in  the  immediately  subsequent  Carboniferous 
Period.  Several  fossil  Amphibia  with  five  digits  have  already 
been  found  in  the  strata  of  the  latter  period.  Fossil  foot- 
prints of  the  same  animals  are  very  numerous  in  the 
Trias  (Cherotheriun). 

The  great  significance  of  the  five  digits  depends  on  the 
fact  that  this  number  has  been  transmitted  from  the 
Amphibia  to  all  higher  Vertebrates.  It  would  be  impossible 
to  discover  any  reason  why  in  the  lowest  Amphibia,  as  well 
as  in  Reptiles  and  in  higher  Vertebrates  up  to  Man, 
there  should  always  originally  be  five  digits  on  each  of  the 
anterior  and  posterior  limbs,  if  we  denied  that  heredity 
from  a  common  five-fingered  parent-form  is  the  efficient 
cause  of  this  phenomenon  :  heredity  can  alone  account  for 
it.  In  many  Amphibia,  certainly,  as  well  as  in  many  higher 
Vertebrates,  we  find  less  than  five  digits.  But  in  all  these 
cases  it  can  be  shown  that  separate  digits  have  retrograded, 
and  have  finally  been  completely  lost. 

The  causes  which  effected  the  development  of  the  five- 
fingered  foot  of  the  higher  Vertebrates  in  this  Amphibian 
parent-form  from  the  many-fingered  foot,  must  certainly  be 
found  in  the  adaptation  to  the  totally  altered  functions 
which  the  limbs  had  to  discharge  during  the  transition  from 
an  exclusively  aquatic  life  to  one  which  was  partially 
terrestrial.  While  the  many-fingered  fins  of  the  Fish  had 
previously  served  almost   exclusively   to  propel  the   body 


FINS   AND   FINGERS.  125 

through  the  water,  they  had  now  also  to  afford  support  to 
the  animal  while  creeping  upon  land.  This  effected  a 
modification  both  of  the  skeleton  and  of  the  muscles  of 
the  limbs.  The  number  of  fin  rays  was  gradually  lessened, 
and  was  finally  reduced  to  five.  These  five  remaining 
rays  now,  however,  developed  more  vigorously.  The  soft 
cartilaginous  rays  became  hard  bones.  The  rest  of  the 
skeleton  also  became  considerably  more  firm.  The  move- 
ments of  the  body  became  not  only  more  vigorous,  but 
also  more  varied.  The  separate  portions  of  the  skeleton 
system,  and  consequently  those  of  the  muscular  system  also, 
became  more  and  more  differentiated.  Owing  to  the  intimate 
correlation  of  the  muscular  to  the  nervous  system,  the  latter 
also  naturally  made  marked  progress  in  point  of  function 
and  structure.  We  therefore  find  that  the  brain  is  very 
much  more  developed  in  the  higher  Amphibia  than  in 
Fishes,  in  Mud-fishes,  and  in  the  lower  Amphibia. 

The  organs  which  are  most  modified  in  consequence  of 
an  amphibious  mode  of  life  are,  as  we  have  already  seen  in 
the  Double-breathers  (Dipnewsta),  those  of  respiration  and 
of  the  circulation  of  the  blood.  The  first  advance  in 
organization  necessitated  by  the  transition  from  aquatic  to 
terrestrial  habits  of  life  was,  of  course,  the  formation  of  an 
air-breathing  organ,  a  lung.  This  developed  directly  from 
the  swimming-bladder  which  these  animals  had  inherited 
from  the  Fishes.  At  first  the  function  of  this  organ  would 
be  quite  subordinate  to  the  more  ancient  organ,  used  for  the 
respnation  of  water,  the  gills.  Hence  we  find  that  the 
lowest  Amphibia,  the  Gilled  Amphibia,  like  the  Dipneusta, 
spend  the  greater  part  of  their  lives  in  the  water,  and  that 
accordingly  they  breathe  water  through  gills.     It  is  only 


126  THE   EVOLUTION   OF  MAN. 

for  brief  intervals  that  they  rise  to  the  surface  of  the  water 
or  creep  out  of  the  water  on  to  the  land  ;  and  at  these  times 
they  breathe  air  through  lungs.  Some,  however,  of  the 
Tailed  Amphibians,  the  Axolotl  and  the  Salamander,  live 
exclusively  in  the  water  only  when  young,  and  afterwards 
usually  remain  on  land.  In  the  adult  state  they  breathe 
only  air  through  lungs.  This  is  also  the  case  with  the  most 
highly  developed  Amphibians,  the  Frog-amphibia  (Frogs  and 
Toads) ;  some  of  the  latter  have  even  entirely  lost  the 
gilled  larval  form.153  The  same  is  true  of  a  few  small 
snake-like  Amphibia,  the  Ccecilise,  which,  like  earth-worms, 
live  in  the  ground. 

The  high  degree  of  interest  attached  to  the  natural 
history  of  the  Amphibian  class  is  especially  due  to  the  fact 
that  they  hold  a  position  exactly  intermediate  between  the 
higher  and  the  lower  Vertebrates.  While  the  lower  Am- 
phibia are  in  their  whole  organization  directly  allied  to  the 
Dipneusta  and  the  Fishes,  living  mostly  in  the  water  and 
respiring  water  through  gills,  the  higher  Amphibia  are  no 
less  directly  related  to  the  Amnion  Animals,  for,  like  the 
latter,  they  live  mostly  on  land,  and  breathe  air  through 
lungs.  But  when  young  the  higher  forms  resemble  the  lower, 
and  only  attain  their  own  higher  degree  of  development 
after  undergoing  complete  modification.  The  individual 
germ-history  of  most  higher  Amphibians  still  accurately 
reproduces  the  tribal  history  of  the  whole  class  ;  and  the 
various  stages  of  modification  which  were  necessitated  in 
certain  low  Vertebrates  by  the  transition  from  aquatic  to 
terrestrial  habits  during  the  Devonian  or  Carboniferous 
Period,  are  still  to  be  seen  every  spring  in  each  Frog  as  it 
develops  from  the  egg  in  our  ditches  and  pools. 


IMPORTANCE   OF   AMPHIBIA. 


127 


Like  the  Tailed  Salamanders  (Fig.  193),  each  common 
Frog  emerges  from  the  egg  in  a  larval  form,  totally  different 
from  that  of  the  full-grown  Frog  (Fig.   194).     The  short 


Fig.  193. — Larva  of  Spotted  Land-Newt  (Salamandra  maculata),  from 
the  ventral  side.  In  the  centre  a  yelk-sac  yet  protrudes  from  the  intestine. 
The  external  gills  are  prettily  branched  and  tree-like.  The  two  pairs  of 
limbs  are  yet  very  small. 

Fig.  194. — Larva  of  the  Common  Grass-Frog  (Rana  temporaria),  a  so- 
called  tadpole:  ra,  mouth;  n,  a  pair  of  suction  cups  used  in  clinging  to  stones ; 
tZ,  skin-fold,  which  gives  rise  to  the  gill-roof ;  behind  are  the  gill-openings, 
from  which  the  gill  branches  protrude ;  s,  tail-muscles ;  /,  skin-fold  of  the 
tail,  forming  a  float. 

trunk  is  produced  into  a  long  tail,  which  in  form  and  struc- 
29 


128  THE   EVOLUTION   OF   MAN. 

ture  resembles  the  tail  of  a  Fish  (s).  At  first  it  has  no 
limbs.  Respiration  is  accomplished  solely  by  gills,  which 
are  at  first  external  (Jc)  and  afterwards  internal.  Corre- 
spondingly, the  heart  is  also  of  the  same  form  as  in  the 
Fishes,  and  consists  of  only  two  compartments — an  auricle, 
which  receives  the  venous  blood  of  the  body,  and  a  ven- 
tricle, which  drives  it  through  the  arterial  bulb  into  the 
gills. 

Numbers  of  these  fish-like  Frog  larvse,  or  "  tadpoles,"  as 
they  are  called,  swim  about  every  spring  in  all  ponds  and 
pools,  using  their  muscular  tails  for  propulsion,  just  as  is 
done  by  Fishes  and  larval  Ascidians.  The  remarkable 
transformation  of  the  fish-like  form  into  that  of  the  Frog 
does  not  take  place  till  after  the  tadpole  has  grown  to  a 
certain  size.  From  the  throat  grows  a  closed  sac  which 
develops  into  a  pair  of  large  sacs;  these  are  the  kings. 
The  simple  chamber  of  the  heart  is  divided  into  two  auricles, 
owing  to  the  formation  of  a  partition  wall,  and  simul- 
taneously considerable  changes  of  structure  occur  in  the 
main  arterial  trunks.  Previously  all  the  blood  passed  from 
the  heart-chamber  through  the  aorta  arches  into  the  gills ; 
but  only  part  of  it  now  passes  to  the  gills,  while  another 
part  passes  through  the  newly  formed  lung  arteries  into  the 
lunffs.  From  the  lun^s  arterial  blood  returns  into  the  left 
auricle  of  the  heart,  while  the  venous  blood  of  the  body 
collects  in  the  right  auricle.  As  both  of  the  auricles  open 
into  the  simple  ventricle,  the  latter  contains  mixed  blood. 
The  fish-like  form  has  now  passed  into  the  Dipneusta  form. 
During  the  further  course  of  modification  the  gills,  with 
the  gill- vessels,  are  entirely  lost,  and  respiration  is  now  per- 
formed by  the  lungs  alone.     Yet  later,  the  long  tail  is  also 


GILLED   BATRACHIANS.  1 29 

rejected,  and  the  Frog  now  leaps  about  on  the  land  on  legs 
which  have  sprouted  in  the  mean  time.150 

This  remarkable  metamorphosis  of  the  higher  Amphibia 
is  very  instructive  in  its  bearing  on  Man's  ancestral  history, 
and  is  especially  interesting  owing  to  the  fact  that  the 
various  groups  of  extant  Amphibia  have  remained  stationary 
at  various  stages  of  their  tribal  history,  which,  in  accord- 
ance with  the  fundamental  law  of  Biogeny,  are  reproduced 
in  this  germ-history.  First,  there  is  a  very  low  order  of 
Amphibia,  the  Gilled  Batrachians  (Sozobranehia),  which,  like 
Fishes,  retain  their  gills  throughout  life.  To  this  order 
belong,  among  others,  the  well-known  blind  "  Olm  "  of  the 
Adelsberg  Cave  (Proteus  anguineus),  the  Mud-eel  of  South 
Carolina  (Siren  lacertina),  and  the  Axolotl  of  Mexico  (Sire- 
don  pisdformis;  Plate  XIII.  Fig.  1).  All  these  Gilled 
Batrachians  are  fish-like  animals  with  long  tails,  and  in 
point  of  respiratory  organs  and  of  circulation  of  the  blood 
they  remain  throughout  life  stationary  at  the  Dipneusta 
stage.  They  possess  both  gills  and  lungs,  and  can  either 
respire  water  through  the  gills  or  air  through  the  lungs,  as 
occasion  requires.  In  another  order,  the  Salamanders,  the 
gills  are  lost  during  metamorphosis,  and  in  the  adult  state  air 
only  is  breathed  through  lungs.  This  order  bears  the  name 
of  Tailed  Batrachians  (Sozara)  because  they  retain  the  tail 
throughout  life.  To  this  order  belong  the  common  Water- 
Newts  (Triton)  which  swarm  in  all  ponds  during  the 
summer,  and  the  black,  yellow-speckled  Land-Salamanders 
(Salamaadra)  found  in  damp  woods  (Plate  XIII.  Fig.  2). 
The  latter  are  among  the  most  remarkable  of  our  indigenous 
animals,  sundry  anatomical  characters  proving  them  to  be 
very   ancient  and    highly   conservative   Vertebrates.151     A 


I30  THE   EVOLUTION    OF   MAN. 

few  Tailed  Batrachians  retain  the  gill-opening  in  the  side 
of  the  neck,  though  the  gills  themselves  are  lost  (Meno- 
poma).  If  the  larvse  of  the  Salamanders  (Fig.  193)  and 
Tritons  are  compelled  to  remain  in  water,  and  not  allowed 
to  get  on  land,  they  may,  under  favourable  conditions,  be 
made  to  retain  their  gills.  In  this  fish-like  condition  they 
become  sexually  mature,  and  will  throughout  life  remain 
compulsorily  in  the  lower  stage  of  development  of  the 
Gilled  Batrachians.  The  opposite  experiment  was  made 
some  years  ago  in  the  case  of  the  Mexican  Gilled  Batra- 
chian,  the  fish-like  Axolotl  (Siredon  pisciformis ;  Plate 
XIII.  Fig.  1).  This  animal  had  previously  been  regarded 
as  a  permanent  Gilled  Batrachian,  remaining  throughout 
life  in  this  fish-like  condition.  But  of  the  hundreds  of 
these  animals  kept  in  the  Jardin  des  Plantes  at  Paris,  a  few 
individuals,  for  some  unknown  reason,  crept  to  land,  lost 
their  gills,  and  changed  into  a  form  closely  allied  to  that  of 
the  Salamander  (Amblystoma,  Fig.  2).  In  this  state  they 
became  sexually  mature.152  This  phenomenon,  which  at 
first  excited  a  lively  interest,  has  since  been  repeatedly 
observed  with  care.  Zoologists  regarded  the  fact  as  some- 
thing peculiarly  wonderful,  though  each  spring  every 
common  Frog  and  Salamander  passes  through  the  same 
modification.  In  these  animals  we  can  in  the  same  way 
follow  each  step  in  the  significant  metamorphosis  of  the 
aquatic  and  gill-respiring  animal  into  the  terrestrial  and 
lung-respiring  animal.  That  which  thus  takes  place  in  the 
individual  during  germ-evolution,  took  place  in  the  same 
way  in  the  whole  class  during  the  course  of  its  tribal 
history. 

The  metamorphosis  which  takes  place  in  the  third  order 


haeckel's  evolution  of  man. 


PLATE  XII. 


ty* 


Cfrafo<7us 
Ibrskri 


HAECKELS    EVOLUTION    OF    MAN. 


PLATE  XIII. 


Fy.2 


\\ 


.v.; 


Fig.  r.  Siredon  piriformis.  Fig.  2.   Salamandra  ma 


culata. 


TAILED  BATRACHIANS  AND  FEOG  BATRACHIANS.   131 

of  Amphibia,  the  Frog  Batrachians  (Batrachia,  or  Anura), 
is  yet  more  complete  than  in  the  Salamanders.  To  these 
belong  all  the  various  kinds  of  Toads,  Water-frogs,  Tree- 
frogs,  etc.  In  the  course  of  transformation  these  lose  not 
only  the  gills,  but  also  the  tail,  which  drops  off  in  some 
cases  earlier,  in  others  later.  In  this  respect  the  various 
species  differ  somewhat  from  one  another.  In  most  Frog 
Batrachians  the  larvre  drop  the  tail  very  early,  and  the 
tail-less  frog-like  form  subsequently  grows  considerably 
larger.  Other  species,  on  the  contrary,  as,  for  instance,  the 
Pseudes paradoxus  of  Brazil,  as  also  an  European  Toad  (Pelo- 
bates fuscus)  remain  for  a  very  long  time  in  the  fish  form, 
and  retain  a  lengthy  tail  till  they  have  almost  attained 
their  full  size;  hence,  after  their  metamorphosis  is  com- 
pleted, they  appear  much  smaller  than  before.  The  opposite 
extreme  is  seen  in  some  Frogs  but  recently  brought  under 
notice,  which  have  lost  the  whole  of  their  historic  meta- 
morphoses, and  in  which  no  tailed  and  gilled  larva  emerges 
from  the  egg,  but  the  perfect  Frog,  without  tail  or  gills. 
These  Frogs  inhabit  isolated  oceanic  islands,  the  climate 
of  which  is  very  dry,  and  which  are  often  for  a  con- 
siderable length  of  time  without  fresh  water.  As  fresh 
water  is  indispensable  for  gill-respiring  tadpoles,  these  Frogs 
have  adapted  themselves  to  this  local  deficiency  and  have 
entirely  relinquished  their  original  metamorphosis,  e.g., 
Ilylodes  martinicensis.153 

The  ontogenetic  loss  of  gills  and  tail  in  Frogs  and  Toads 
can  of  course  only  be  phylogenetically  explained  as  owing 
to  the  fact  that  these  animals  have  descended  from  lone;- 
tailed  salamander-like  Amphibians.  This  is  also  proved 
beyond  doubt  by  the  Comparative   Anatomy  of  the  two 


132  THE    EVOLUTION  OF   MAN. 

groups.  This  remarkable  transformation  is,  in  other  respects 
also,  of  general  interest,  as  throwing  a  flood  of  light  upon  the 
Phylogeny  of  the  Tail-less  Apes  and  of  Man.  Man's  ances- 
tors were  also  long-tailed  gill-breathing  animals,  resembling 
Gilled  Batrachians,  as  is  irrefutably  demonstrated  by  the 
tail  and  the  gill  arches  in  the  human  embryo. 

During  the  Palaeozoic  Epoch,  and  probably  in  the  Car- 
boniferous Period,  there  is  no  doubt  that  the  Amphibian 
class  embraced  a  series  of  forms  which  must  be  regarded  as 
direct  ancestors  of  Mammals,  and  so  of  Man.  On  grounds 
derived  from  Comparative  Anatomy  and  Ontogeny,  we  must 
not,  however,  look  for  these  Amphibian  ancestors  of  ours — 
as  might  perhaps  be  supposed — among  the  Tail-less  Frog 
Batrachians,  but  only  among  the  lower  Tailed  Amphibians. 
We  can  with  certainty  point  to  at  least  two  extinct  Batra- 
chian  forms  as  direct  ancestors  of  Man,  as  the  thirteenth 
and  fourteenth  stages  in  our  pedigree.  The  thirteenth 
ancestral  form  must  have  been  closely  allied  to  the  Double- 
breathers  (Dipneusta),  must,  like  these,  have  possessed  per- 
manent gills,  but  must  have  been  already  characterized  by 
having  five  digits  on  each  foot ;  and  were  they  still  living  we 
should  place  them  in  the  group  of  Gilled  Batrachians,  with 
the  Proteus  and  the  Axolotl  (Plate  XIII.  Fig.  1).  The 
fourteenth  ancestral  form,  on  the  other  hand,  must  indeed 
have  retained  the  long  tail,  but  must  have  lost  the  gills,  and 
hence  the  nearest  allied  forms  among  extant  Tailed  Batra- 
chians would  be  the  Water-Newts  and  Salamanders 
(Plate  XIII.  Fig.  2).  Indeed,  in  the  year  1725  the  fossil 
skeleton  of  one  of  these  extinct  Salamanders  (closely  allied 
to  the  present  giant  Salamander  of  Japan)  was  described 
by   the   Swiss    naturalist,    Scheuchzer,  as   the  skeleton   of 


PRIMITIVE   AMNION   ANIMALS.  1 33 

a  fossil  Man  dating  from  the  Deluge !  ("  Homo  diluvii 
testis."154) 

As  the  vertebrate  form  occurring  in  our  pedigree  imme- 
diately after  these  Batrachian  ancestors — and,  therefore,  as 
the  fifteenth  stage — let  us  now  examine  a  lizard-like  animal, 
of  which  no  fossil  remains  have  been  obtained,  and  which 
is  not  even  proximately  represented  in  any  extant  animal 
form,  but  the  former  existence  of  which  we  may  infer  with 
the  utmost  certainty  from  certain  comparative  anatomical 
and  ontogenetical  facts.  This  important  animal  form  we 
will  call  the  Protamnion,  or  Primitive  Amniotic  animal. 
All  Vertebrates  higher  than  the  Amphibia — that  is,  the  three 
classes  of  Reptiles,  Birds,  and  Mammals — are  so  essentially 
distinct  in  their  whole  structure  from  all  the  lower  Verte- 
brates which  we  have  as  yet  considered,  and,  on  the  other 
hand,  have  so  much  in  common,  that  we  may  class  them 
together  in  one  group  as  Amnion  Animals  (Amniota).  It  is 
only  in  these  three  classes  of  animals  that  we  find  that 
remarkable  envelope  of  the  embryo  known  as  the  amnion. 
(Cf.  vol.  i.  p.  386.)  The  latter  must  probably  be  regarded  as 
a  kenogenetic  adaptation,  as  caused  by  the  sinking  of  the 
embryo  into  the  yelk-sac.155 

All  known  Amnion  Animals,  all  Reptiles,  Birds,  and 
Mammals  (Man  included),  coincide  in  so  many  important 
points  of  organization  and  development  that  we  are  fully 
justified  in  asserting  their  common  descent  from  a  single 
parent  form.  If  the  testimony  of  Comparative  Anatomy 
and  Ontogeny  is  entirely  unquestionable  in  any  point,  it  is 
certainly  so  here.  For  all  the  special  peculiarities  and 
characters,  which  appear  accompanying  and  following  the 
formation  of  the    amnion,   and  which   we  Found    in   the 


134  THE   EVOLUTION   OF  MAN. 

development  of  the  human  embryo;  all  the  many  peculiari- 
ties in  the  development  of  the  organs  which  we  shall 
presently  notice  in  detail ;  and,  finally,  the  chief  special 
arrangements  of  the  internal  structure  of  the  body  in  all 
fully  developed  Amnion  Animals;  all  these  so  clearly  demon- 
strate the  common  origin  of  all  Amnion  Animals  from  a 
single  extinct  parent-form,  that  it  is  impossible  to  conceive 
their  origin  as  polyphyletic,  and  that  they  originated  from 
several  independent  parent-forms.  This  unknown  common 
parent-form  is  the  Primitive  Amnion  Animal  {Protam- 
nion). In  external  appearance  the  Protamnion  was  most 
probably  an  intermediate  form  between  the  Salamanders 
and  the  Lizards. 

It  was  probably  during  the  Permian  Period  that  the 
Protamnion  originated ;  perhaps  at  the  beginning,  perhaps 
at  the  close  of  that  period.  This  we  know  from  the  fact 
that  the  Amphibia  did  not  attain  their  full  development  till 
the  Carboniferous  Period,  and  that  toward  the  close  of  the 
Permian  the  first  fossil  Reptiles  make  their  appearance — 
or,  at  least,  fossils  (Proterosaurus,  Rhopalodon)  which  must 
in  all  probability  be  referred  to  lizard-like  Reptiles.  Among 
the  great  and  pregnant  modifications  of  the  vertebrate 
organization  determined  during  this  period  by  the  develop- 
ment of  the  first  Amnion  Animals  from  salamander-like 
Amphibians,  the  three  following  are  especially  important : 
the  total  loss  of  water-breathing  gills  and  modification  of 
the  gill-arches  into  other  organs ;  the  formation  of  the 
allantois,  or  primitive  urinary  sac;  and,  finally,  the  develop- 
ment of  the  amnion. 

The  total  loss  of  the  respiratory  gills  must  be  regarded 
as  one  of  the   most  prominent  characters  of  all  Amnion 


EVOLUTION   OF   AMNION   ANIMALS.  135 

Animals.  All  these,  even  such  as  live  in  the  water,  e.g., 
whales,  respire  only  air  through  lungs,  never  water  through 
gills.  While  all  Amphibians,  with  very  few  exceptions,  in 
the  young  state  retain  their  gills  for  a  longer  or  shorter 
period,  and  breathe  through  gills  for  some  time  (if  not 
always),  from  this  point  gill-respiration  entirely  ceases. 
Even  the  Protamnion  must  have  entirely  ceased  to  breathe 
water.  The  gill-arches,  however,  remain,  and  develop 
into  very  different  organs  (partly  rudimentary) ;  into  the 
various  parts  of  the  tongue-bone,  into  certain  portions  of  the 
jaw  apparatus,  the  organ  of  hearing,  etc.  But  no  trace  of 
gill-leaves,  of  real  respiratory  organs  on  the  gill-arches,  are 
ever  found  in  the  embryo  of  Amnion  Animals. 

With  this  total  loss  of  the  gills  is  probably  connected 
the  formation  of  another  organ,  which  we  have  already 
described  as  occurring  in  human  Ontogeny ;  this  is  the 
allantois,  or  primitive  urinary  sac.  (See  vol.  i.  p.  370.)  In 
all  probability  the  urinary  bladder  of  the  Dipneusta  is  to  be 
regarded  as  the  first  beginning  of  the  allantois.  Even  in 
the  American  Mud-fish  (Lepidosiren)  we  find  an  urinary 
bladder,  which  grows  from  the  lower  wall  of  the  posterior 
extremity  of  the  intestine,  and  serves  as  a  receptacle  for 
the  renal  secretions.  This  organ  has  been  inherited  by  the 
Amphibia,  as  may  be  seen  in  any  Frog.  But  it  is  only  in 
the  three  higher  Vertebrate  classes  that  the  allantois  attains 
a  special  development ;  in  these  it  protrudes  at  an  early 
period  from  the  body  of  the  embryo,  forming  a  large  sac 
filled  with  liquid,  and  traversed  by  a  considerable  number 
of  large  blood-vessels.  This  sac  also  discharges  a  portion  of 
the  nutritive  functions.  In  the  higher  Mammals  and  in 
Man  the  allantois  afterwards  forms  the  placenta. 


I36  THE   EVOLUTION    OF   MAN. 

The  formation  of  the  amnion  and  the  allantois,  together 
with  the  total  loss  of  the  gills  and  the  exclusive  adoption 
of  lung-respiration,  are  the  most  important  characters  by 
which  all  Amnion  Animals  are  distinguished  from  the  lower 
Vertebrates  which  we  have  been  considering.  In  addition 
to  these  there  are  a  few  subordinate  characters  which  are 
constantly  inherited  by  Amnion  Animals,  and  are  altogether 
wanting  in  animals  without  an  amnion.  One  striking  em- 
bryonic character  of  the  Amnion  Animals  is  the  great  curva- 
ture of  the  head  and  neck  of  the  embryo.  In  the  Anamnia 
the  embryo  is  from  the  first  either  nearly  straight,  or  else 
the  whole  body  is  bent  in  a  sickle-shaped  curve  corre- 
sponding to  the  curvature  of  the  yelk  sac,  to  which  the 
embryo  is  attached  by  its  ventral  surface ;  but  there  are 
no  marked  angles  in  the  longitudinal  axis  (Plate  VI. 
Fig.  F).  In  all  Amnion  Animals,  on  the  contrary,  the 
body  is  very  noticeably  bent  at  an  early  age,  so  that  the 
back  of  the  embryo  is  much  arched  outwards,  the  head 
pressed  almost  at  right  angles  against  the  breast,  and  the 
tail  inclined  on  to  the  abdomen.  The  tail  extremity,  as  it 
bends  inwards,  approaches  so  near  to  the  frontal  side  of 
the  head,  that  the  two  often  nearly  touch  (PJates  VI.  and 
VII.).  This  striking  triple  curvature  of  the  embryonic 
body,  which  has  already  been  considered  when  Ave  studied 
the  Ontogeny  of  Man,  and  in  which  we  distinguished  the 
skull-curve,  neck-curve,  and  tail-curve  (vol.  i.  p.  371),  is  a 
characteristic  peculiarity  common  to  the  embryos  of  all 
Reptiles,  Birds,  and  Mammals.  But  in  the  formation  of  many 
internal  organs  also,  an  advance  is  observable  in  all  the 
Amnion  Animals  which  ranks  them  above  the  highest  of 
the  non-amnionate  forms.     Above  all,  a  partition  wall  forms 


MAN   AS   AN   AMNION   ANIMAL.  1 37 

within  the  simple  ventricle  of  the  heart,  dividing  it  into  a 
right  and  a  left  ventricle.  In  connection  with  the  complete 
metamorphosis  of  the  gill-arches,  a  further  development  of 
the  organ  of  hearing  takes  place.  A  considerable  advance 
is  also  noticeable  in  the  development  of  the  brain,  the  skele- 
ton, the  muscular  system,  and  other  parts.  Finally,  the 
reconstruction  of  the  kidneys  must  be  regarded  as  a  most 
important  modification.  In  all  the  lower  Vertebrates  as  yet 
considered,  we  have  found  the  primitive  kidneys,  which 
appear  very  early  in  the  embryos  of  all  higher  Vertebrates 
up  to  Man,  acting  as  a  secretory  or  urinary  apparatus.  In 
Amnion  Animals,  however,  these  early  primitive  kidneys 
lose  their  function  at  an  early  period  of  embryonic  life,  and 
it  is  assumed  by  the  permanent  "  secondary  kidneys,"  which 
grow  out  of  the  terminal  portion  of  the  primitive  kidney 
ducts. 

Looking  back  at  the  whole  of  these  characters  of  Amnion 
Animals,  it  is  impossible  to  doubt  that  all  animals  of  this 
group,  all  Reptiles,  Birds,  and  Mammals,  had  a  common 
origin,  and  constitute  a  single  main  division  of  kindred 
forms.  To  this  division  belongs  our  own  race.  In  his 
whole  organization  and  germ-history  Man  is  a  true  Amnion 
Animal,  and,  in  common  with  all  other  Amniota,  has 
descended  from  the  Protamnion.  Although  this  whole 
group  originated  at  the  end,  or  perhaps  even  in  the  middle, 
of  the  Pakeozoic  Epoch,  it  did  not  attain  its  full  de- 
velopment and  its  full  perfection  till  the  Mesozoic  Epoch. 
The  two  classes  of  Birds  and  Mammals  then  first  appeared. 
Nor  did  the  Reptilian  class  develop  in  its  full  variety 
until  the  Mesozoic  Epoch,  which  is,  therefore,  called  the  "Age 
of  Reptiles."     The  unknown  and  extinct  Protamnion,  the 


I38  THE   EVOLUTION   OF   MAN. 

parent-form  of  the  entire  group,  must  have  been  very  nearly 
allied  to  the  Reptiles  in  its  whole  organization,  even  though 
it  cannot  be  regarded  as  a  true  Reptile  in  the  present 
meaning  of  the  term.  Of  all  known  Reptiles,  certain  Lizards 
are  most  nearly  allied  to  the  Protamnion ;  and  in  the 
outward  form  of  its  body  we  may  imagine  the  latter  as 
an  intermediate  form  between  the  Salamander  and  the 
Lizard.156 

The  Comparative  Anatomy  and  Ontogeny  of  the  Am- 
nionate  group  clearly  explains  its  genealogy.  The  group 
which  directly  descended  from  Protamnion  gave  rise  to  two 
divergent  branches.  The  first  of  these,  which  will  in  future 
receive  our  whole  attention,  forms  the  Mammalian  group. 
The  other  branch,  which  assumed  an  entirely  different  course 
of  progressive  development,  and  which  is  connected  with 
the  mammalian  branch  only  as  the  root,  is  the  compre- 
hensive group  constituted  by  Reptiles  and  Birds.  The  two 
latter  forms  may  be  classed  together  as  Monocondylia,  or 
Sauropsides.  The  common  parent-form  of  these  is  an 
extinct  lizard-like  Reptile.  From  this,  the  Serpents,  Croco- 
diles, Tortoises,  Dragons,  etc. — in  short,  all  the  various  forms 
of  the  Reptilian  group — developed  in  different  directions. 
The  remarkable  group  formed  by  the  Birds  also  developed 
directly  from  an  offshoot  of  the  Reptilian  group,  as  is  now 
definitely  proved.  Down  to  a  late  time  the  embryos  of 
Reptiles  and  of  Birds  are  yet  identical,  and  even  later  they 
are  in  some  respects  surprisingly  similar.  (See  Plate  VI.  Fig. 
T  and  C.)  In  their  entire  organization  the  resemblance 
between  the  two  is  so  great  that  no  anatomist  now  denies 
that  the  Birds  originated  from  Reptiles.  The  Mammalian 
line  is  connected  at  its  roots  with  the  Reptilian  line,  but 


GENEALOGY  OF  AMNION  ANIMALS.         1 39 

afterwards  diverged  entirely  from  the  latter,  and  developed 
in  an  entirely  peculiar  direction.  The  highest  result  of  the 
development  of  the  Mammalian  line  is  Man,  the  so-called 
"  Crown  of  Creation." 


CHAPTER  XIX 

THE   PEDIGREE   OF   MAN. 
IV.    Fiiom  the  Primitive  Mammal  to  tue  Ape. 

The  Mammalian  Character  of  Man. —  Common  Descent  of  all  Mammals 
from  a  Single  Parent-form  (Promammalian). — Bifurcation  of  the  Am 
nion  Animals  into  Two  Main  Lines  :  on  the  one  side,  Reptiles  and  Birds, 
on  the  other,  Mammals.— Date  of  the  Origin  of  Mammals  :  the  Trias 
Period. — The  Three  Main  Groups  or  Sub-classes  of  Mammals  :  their 
Genealogical  Relations. — Sixteenth  Ancestral  Stage  :  Cloacal  Animals 
(Monotremata,  or  Ornithodelrphia). — The  Extinct  Primitive  Mammals 
(Promammalia)  and  the  Extant  Beaked  Animals  (Ornithostoma) . — 
Seventeenth  Ancestral  Stage  :  Pouched  Animals  (Marsiqrialia,  or  Didel- 
phia). — Extinct  and  Extant  Pouched  Animals. — Their  Intermediate 
Position  between  Monotremes  and  Placental  Animals. — Origin  and 
Structure  of  Placental  Animals  (Placentalia,  or  Monodelpliia) . — Forma- 
tion of  the  Placenta. — The  Deciduous  Embryonic  Membrane  (Decidua). 
— Group  of  the  Indecidua  and  of  the  Deciduata. — The  Formation  of  the 
Decidua  (vera,  serotina,  reflexa)  in  Man  and  in  Apes. — Eighteenth 
Stage:  Semi-apes  (Prosimicc). — Nineteenth  Stage:  Tailed  Apes  (M eno- 
cerca). — Twentieth  Stage  :  Man-like  Apes  (Anthropoides). — Speechless 
and  Speaking  Men  (Mali.  Homines). 

"  A  century  of  anatomical  research  brings  ns  back  to  the  conclusion  of 
Linnaeus,  the  great  lawgiver  of  systematic  zoology,  that  man  is  a  member 
of  the  same  order  as  the  apes  and  lemurs.  Perhaps  no  order  of  mammals 
presents  us  with  so  extraordinary  a  series  of  gradations  as  this,  leading  us 
insensibly  from  the  crown  and  summit  of  the  animal  creation  down  to 
creatures  from  which  there  is  but  a  step,  as  it  seems,  to  the  lowest,  smallest, 
and  least  intelligent  of  the  placental  mammalia.     It  is  as  if  nature  herself 


"man's  place  in  nature.  141 

had  foreseen  the  arrogance  of  man,  and  with  Roman  severity  had  provided 
that  his  intellect,  by  its  very  triumphs,  should  call  into  prominence  the 
slaves,  admonishing  the  conqueror  that  he  is  but  dust." — Thomas  Huxley 
(1863). 

Among  those  zoological  facts  which  afford  us  points  of 
support  in  researches  into  the  pedigree  of  the  human  race, 
the  position  of  Man  in  the  Mammalian  class  is  one  of  the 
most  important  and  fundamental.  Much  as  zoologists  have 
long  disagreed  in  their  opinions  as  to  Man's  particular  place 
in  this  class,  and  especially  in  their  ideas  of  his  relation  to 
the  most  nearly  related  group,  that  of  the  Apes,  yet  no 
naturalist  has  ever  doubted  that  Man  is  a  genuine  Mammal 
in  the  whole  structure  and  development  of  his  body.  Every 
anatomical  museum,  every  manual  of  Comparative  Anatomy, 
affords  proof  that  the  structure  of  the  human  body  shares 
all  those  peculiarities  which  are  common  to  all  Mammals, 
and  by  which  the  latter  are  definitely  distinguished  from  all 
other  animals. 

Now,  if  we  examine  this  established  anatomical  fact 
phylogenetically,  and  in  the  light  of  the  Theory  of  Descent, 
we  arrive  immediately  at  the  conclusion  that  Man  is  of  a 
common  stock  with  all  the  other  Mammals,  and  springs 
from  a  root  common  to  them.  The  various  characteristics 
in  which  all  Mammals  coincide,  and  in  which  they  differ 
from  all  other  animals,  are,  moreover,  of  such  a  kind,  that  a 
polyphyletic  hypothesis  appears  in  a  special  degree  inad- 
missible in  their  case.  It  is  inconceivable  that  all  existing 
and  extinct  Mammals  have  sprung  from  several  different 
and  originally  separate  root-forms.  We  are  compelled,  if 
we  in  any  way  acknowledge  the  Theory  of  Evolution,  to 
assume   the   monophyletic  hypothesis,  that   all   Mammals, 


142  THE   EVOLUTION   OF   MAN. 

including  Man,  must  be  traced  from  a  single  common  mam- 
malian parent-form.  This  long  extinct  primaeval  root-form 
and  its  immediate  descendants — which  differ  from  each 
other  hardly  more  than  do  several  species  of  one  genus — we 
will  call  Primitive  Mammals  (Promammalia).  As  we  have 
already  seen,  this  root-form  developed  from  the  ancient 
parent-form  of  the  Primitive  Amnion  Animals  in  a  direction 
wholly  different  from  that  followed  by  the  Reptile  group, 
which  afterwards  gave  rise  to  the  more  highly  developed 
class  of  Birds.  The  differences  which  distinguish  Mammals 
on  the  one  side,  from  Reptiles  and  Birds  on  the  other,  are  so 
important  and  characteristic,  that  we  may  quite  safely  as- 
sume a  bifurcation  of  this  kind  in  the  vertebrate  family  tree. 
Reptiles  and  Birds — which  we  classed  together  as  Monocon- 
dylia,  or  Sauropsida — coincide  entirely,  for  instance,  in  the 
characteristic  structure  of  the  skull  and  brain,  which  is 
strikingly  dissimilar  from  that  of  the  same  parts  in  Mam- 
mals. In  Reptiles  and  Birds,  the  skull  is  connected  with  the 
first  cervical  vertebra  (the  atlas)  by  a  single  joint-process 
(condyle)  of  the  occipital  bone ;  in  Mammals,  on  the  con- 
trary (as  in  Amphibians),  the  condyle  is  double.  In  the 
former,  the  under  jaw  is  composed  of  many  parts,  and  is 
connected  with  the  skull  by  a  peculiar  bone  of  the  jaw 
(the  square  bone)  so  as  to  be  movable ;  in  the  latter,  on  the 
contrary,  the  lower  jaw  consists  of  but  two  bone-pieces, 
which  are  directly  attached  to  the  temporal  bone.  Again, 
the  skin  of  the  Sauropsida  (Reptiles  and  Birds)  is  covered 
with  scales  or  feathers,  that  of  the  Mammals  with  hair. 
The  red  blood-cells  of  the  former  are  nucleated,  those  of  the 
latter  non-nucleated.  The  eggs  of  the  former  are  very 
large,  are  provided  with  a  large  nutritive  yelk,  and  undergo 


REPTILES   AND   MAMMALS.  1 43 

discoidal  cleavage  resulting  in  a  Disc-gastrula ;  the  eggs  of 
the  latter  are  very  small,  and  their  unequal  cleavage  results 
in  the  formation  of  a  Hood-gastrula.  Finally,  two  charac- 
ters entirely  peculiar  to  Mammals,  and  by  which  these 
are  distinguished  both  from  Birds  and  Reptiles  and  from  all 
other  animals,  are  the  presence  of  a  complete  diaphragm, 
and  of  the  milk-glands  (mammce),  by  means  of  which  the 
new-born  young  are  nourished  by  the  milk  of  the  mother. 
It  is  only  in  Mammals  that  the  diaphragm  forms  a  transverse 
partition-wall  across  the  body-cavity  (cceloma),  completely 
separating  the  chest  from  the  ventral  cavity.  (Cf.  Plate  V. 
Fig.  16  z.)  It  is  only  among  Mammals  that  the  mother 
nourishes  the  young  with  her  milk  ;  and  the  whole  class  are 
well  named  from  this. 

These  important  facts  in  Comparative  Anatomy  and 
Ontogeny  clearly  show  that  the  tribe  of  Amnion  Animals 
(Amniota)  bifurcated  from  the  very  first  into  two  main 
diverging  lines ;  on  the  one  side,  the  Reptilian  line,  from 
which  the  Birds  afterwards  developed ;  on  the  other  side, 
the  Mammalian  line.  The  same  facts  also  prove  as  indu- 
bitably that  Man  originated  from  the  latter  line.  For  Man, 
in  common  with  Mammals,  shares  all  the  characteristics  we 
have  mentioned,  and  is  distinguished  by  them  from  all 
other  animals.  And,  finally,  these  facts  indicate  as  certainly 
those  advances  in  vertebrate  structure  by  which  one  branch 
of  the  Primitive  Amnion  Animals  developed  into  the  parent- 
form  of  Mammals.  The  most  prominent  of  these  advances 
were  (1)  the  characteristic  modification  of  the  skull  and 
brain ;  (2)  the  formation  of  a  covering  of  hair ;  (3)  the  com- 
plete development  of  the  diaphragm ;  and  (4)  the  formation 
of  the  milk-glands  and  the  adaptation  to  the  suckling  of 


144  THE   EVOLUTION    OF   MAN. 

the  young.     Intimately   connected   with   these,   other   im- 
portant structural  modifications  gradually  occurred. 

The  period  at  which  these  important  advances,  which 
laid  the  first  foundation  of  the  Mammalian  class,  took  place, 
may  most  probably  be  placed  in  the  first  part  of  the 
Mesolithic,  or  Secondary  Epoch,  in  the  Triassic  Period. 
For  the  oldest  known  fossil  remains  of  Mammals  occur  in 
sedimentary  rock-strata  of  the  most  recent  deposits  of  the 
Triassic  Period,  in  the  upper  Keuper.  It  is  possible, 
indeed,  that  the  parent-forms  of  Mammals  may  have 
appeared  earlier  (perhaps  even  at  the  close  of  the  Palaeo- 
lithic Epoch,  in  the  Permian  Period).  But  no  fossil  remains 
of  Mammals  belonging  to  that  period  are  as  yet  known. 
Throughout  the  Mesolithic  Epoch,  throughout  the  Triassic, 
Jurassic,  and  Calcareous  Periods,  fossil  remains  of  Mammals 
are  very  scarce,  and  indicate  a  very  limited  development 
of  the  whole  class.  During  this  Mesolithic  Epoch,  Reptiles 
play  the  chief  part,  and  Mammals  are  of  quite  secondary 
importance.  It  is,  however,  especially  significant  and 
interesting,  that  all  mammalian  fossil  remains  of  the 
Mesozoic  Epoch  belong  to  the  older  and  inferior  division 
of  Pouched  Animals  (Marsupialia),  a  few  probably  even 
to  the  yet  older  division  of  the  Cloacal  Animals  {Mono- 
trema).  Among  them,  no  traces  of  the  third  and  most 
highly  developed  division  of  the  Mammals,  the  Placental 
Animals,  have  as  yet  been  found.  The  last,  to  which  Man 
belongs,  are  much  more  recent,  and  their  fossil  remains  do 
not  occur  till  much  later — in  the  succeeding  Camolithic 
Epoch ;  in  the  Tertiary  Period.  This  paloeontological  fact 
is  very  significant,  because  it  harmonizes  perfectly  with 
that  order  of  the  development  of  Mammals  which  is  un- 


THE 'THREE   MAMMALIAN   GROUPS.  I45 

mistakably  indicated  by  Comparative  Anatomy  and  Onto- 
geny. 

These  show  that  the  whole  Mammalian  class  is  divisible 
into  three  main  groups,  or  sub-classes,  corresponding  to 
three  successive  stages  of  phylogenetic  evolution.  These 
three  stages,  which  consequently  represent  three  important 
ancestral  stages  in  the  human  pedigree,  were  first  dis- 
tinguished in  the  year  1816  by  the  celebrated  French 
zoologist,  Blainville,  who  named  them,  according  to  the 
different  structure  of  the  female  organs  of  reproduction, 
Ornithodelphia,  Didelplvia,  and  Monodelphia  (SsXcpvg, 
which,  being  interpreted,  is  uterus).  It  is  not,  however, 
only  in  the  varied  structure  of  the  sexual  organs  that  these 
three  classes  differ  from  one  another,  but  in  many  other 
respects  also,  so  that  we  can  safely  maintain  the  important 
phylogenetic  statement :  The  Monodelphia,  or  Placental 
Animals,  have  descended  from  the  Didelphia,  or  Pouched 
Animals ;  and  the  latter,  again,  have  descended  from  the 
Cloacal  Animals,  or  Ornithodelphia. 

Accordingly  we  have  now  to  consider,  as  the  sixteenth 
ancestral  stage  in  the  human  pedigree,  the  oldest  and  lowest 
main  group  of  Mammals ;  the  sub-class  of  the  Cloacal 
Animals  (Monotremata,  or  Ornithodelphia).  They  are  so 
named  in  consecpience  of  the  cloaca,  which  they  have  in 
common  with  the  other  lower  Vertebrates.  This  so-called 
cloaca  is  the  common  excretory  channel  for  the  excrement, 
the  urine,  and  the  sexual  products  (Fig.  327).  For,  in 
these  Cloacal  Animals,  the  urinary  duct  and  the  sexual 
canals  yet  open  into  the  posterior  parts  of  the  intestine, 
while  in  all  other  Mammals  they  are  wholly  separated  from 
the  rectum  and  anus,  and  open  by  a  special  orifice  (porus 


I46  THE   EVOLUTION   OF  MAN. 

urogenitals).  The  urinary  bladder  in  the  Monotrernes  also 
opens  into  the  cloaca,  and  is  separate  from  the  two  urinary 
ducts  (Fig.  327,  vo) ;  in  all  other  Mammals  the  latter  open 
directly  into  the  urinary  bladder.  The  structure  of  the 
milk -glands,  by  means  of  which  all  Mammals  suckle  their 
new-born  young  for  a  time,  is  also  quite  peculiar  in 
the  Cloacal  Animals.  In  them  the  milk -gland  has  no 
nipple  which  the  young  animal  can  suck  ;  there  is  only 
a  peculiar  sieve-like  place  in  the  skin,  perforated  with 
holes  through  which  the  milk  passes  out,  and  from  which 
the  young  animal  has  to  lick  it.  For  this  reason  they 
have  also  been  called  Nipple-less  Mammals  (Amasta). 
Again,  the  brain  of  the  Cloacal  Animals  has  remained  at  a 
much  lower  stage  of  development  than  that  of  any  other 
Mammal.  The  fore-brain,  or  cerebrum,  is  so  small  that 
it  does  not  overhang  the  hind- brain,  or  cerebellum.  In  the 
skeleton  (Fig.  196),  the  structure  of  the  shoulder  girdle,  as 
well  as  of  other  parts,  is  remarkable,  differing  entirely  from 
the  same  part  in  other  Mammals,  and  resembling  rather 
those  of  the  lower  Vertebrates,  especially  Reptiles  and 
Amphibians.  Like  the  latter,  the  Cloacal  Animals  have  a 
well-developed  coracoid  bone  (coracoideum),  a  strong  bone 
uniting  the  shoulder-blade  with  the  breast-bone.  In  all 
other  Mammals  the  coracoid  bone  (as  in  Man)  has  degene- 
rated, has  coalesced  with  the  shoulder-blade,  and  appears 
only  as  an  insignificant  process  of  the  latter.  These  and 
many  other  less  striking  peculiarities  prove  beyond  doubt 
that  the  Cloacal  Animals  occupy  the  lowest  rank  among 
Mammals,  and  represent  a  direct  intermediate  form  between 
the  Protamnia  and  other  Mammals.  All  these  marked  Am- 
phibian characters  must  have  been  present  in  the  parent 


EXTANT  CLOACAL  ANIMALS.  147 

form  of  the  whole  vertebrate  class,  in  the  Primitive 
Mammal,  by  which  they  must  have  been  inherited  from 
the  Primitive  Amnion  Animals. 

During  the  Triassic  and  Jurassic  Periods,  the  sub-class 
of  the  Cloacal  Animals  seems  to  have  been  represented  by 
many  Primitive  Mammals  of  very  varied  form.     At  present 
it  is  represented   only   by   two   isolated  members,  which 
are  grouped  together  as  the  Beaked  Animal  family  (Orni- 
thostoma).     Both  of  these  are  confined  to  Australia  and  the 
neighbouring  island  of  Van  Diemen's  Land,  or  Tasmania ; 
both  are  becoming  less  numerous  year  by  year,  and  will 
soon  be  classed,  with  all  their  blood  relations,  among  the 
extinct  animals  of  our  globe.     One  of  these  forms  passes 
its  life  swimming  about  in  rivers,  and  builds  subterranean 
dwellings  on  the  banks :    this   is   the  well-known  Duck- 
billed Platypus  (Omithorhynchiis  paradoxus) :   it  is  web- 
footed,  has  a  thick,  soft  skin,  and  broad,  fiat  jaws,  which 
very  much  resemble   a  duck's   bill  (Figs.  195,  10G).     The 
other  form,  the  Porcupine  Ant-eater  (Echidna  hystrix),  much 
resembles  the  Ant-eaters,  in  its  mode  of  life,  in  the  cha- 
racteristic form  of  its  slender  snout,  and  in  the  great  length 
of  its  tongue ;  it  is  covered  with  prickles,  and  can  roll  itself 
up  into  a  ball  like  a  hedgehog.     Neither  of  these  extant 
Beaked   Animals  possesses  true  bony  teeth,  and,  in   this 
point,   they  resemble  the  Toothless  Mammals  (Edentata). 
The  absence  of  teeth,  together  with  other  peculiarities  of 
the  Ornithostomata,  is  probably  the  result  of  comparatively 
recent  adaptation.     Those  extinct  Cloacal  Animals  which 
embraced  the  parent-forms  of  the  whole  Mammalian  class, 
the  Promammalia,  must  certainly  have  been  provided  with 
a  developed  set  of  teeth,  inherited  from  Fishes.157     Some 


148 


THE   EVOLUTION   OF   MAN. 


Fig.  195.— The  Duck-billed  Platy, 
pus  (Omithorhynchus  paradoxus). 
Fig.  196.— Skeleton  of  Platypus. 


POUCHED   ANIMALS.  1 49 

small  single  molars,  found  in  the  uppermost  strata  of 
the  Keuper  formation  in  England  and  Wiirtemberg,  and 
which  are  the  oldest  known  vertebrate  remains,  probably 
belong  to  these  primaeval  Promammalia.  These  teeth,  by 
their  form,  indicate  species  that  lived  on  insects ;  the  species 
has  been  called  Microlestes  antiquus.  Teeth  belonging  to 
another  closely  allied  Primitive  Mammal  (Dromatherium 
silvestre)  have  recently  been  discovered  in  the  North 
American  Trias. 

On  the  one  hand,  the  still  extant  Beaked  Animals,  and,  on 
the  other,  the  parent-forms  of  the  Pouched  Animals  (Mar- 
swpialia,  or  Didelphia),  must  be  regarded  as  representing 
two  distinct  and  divergent  lines  of  descent  from  the  Pro- 
mammalia.  This  second  Mammalian  sub-class  is  very 
interesting  as  a  perfect  link  between  the  two  other  sub- 
classes. While  the  Pouched  Animals,  on  the  one  side,  retain 
many  of  the  characters  of  the  Cloacal  Animals,  they  also, 
on  the  other,  possess  many  placental  characters.  A  few 
characters  are  quite  peculiar  to  Pouched  Animals  alone ; 
such,  for  instance,  is  the  structure  of  the  male  and  female 
sexual  organs,  and  the  form  of  the  lower  jaw  The  dis- 
tinctive feature  of  the  latter  in  these  Pouched  Animals  is  a 
peculiar  hook-shaped  bony  process,  passing  inward  hori- 
zontally from  the  angle  of  the  lower  jaw.  As  neither 
Cloacal  Animals  nor  Placental  Animals  have  this  process, 
this  structui'e  is  alone  sufficient  to  distinguish  the  Pouched 
Animals  (Marsupkdia).  Nearly  all  the  known  mammalian 
fossils  from  the  Jurassic  and  Cretaceous  formation  are  lower 
jaws.  Our  whole  knowledge  of  numerous  mesolithic  mam- 
malia, the  former  existence  of  which  would  otherwise  never 
have  been  known,  is   solely  derived  from  their  fossilized 


I50  THE   EVOLUTION   OF  MAN. 

lower  jaws,  no  fragment  of  the  rest  of  their  bodies  having 
been  reserved.  According  to  the  logic  usually  applied  to 
palaeontology  by  the  "  exact "  opponents  of  the  theory  of 
evolution,  the  inference  drawn  from  this  fact  would  be 
that  these  Mammals  had  no  bones  except  lower  jaws.  The 
remarkable  circumstance  is,  after  all,  very  easily  accounted 
for.  The  lower  jaw  of  Mammals  being  a  solid  and  excep- 
tionally hard  bone,  but  very  loosely  attached  to  the  skull,  it 
is  easily  detached  from  the  carcase  as  the  latter  is  carried 
down  by  some  river,  and,  falling  to  the  bottom,  is  retained 
in  the  mud.  The  rest  of  the  carcase  is  carried  on  further, 
and  is  gradually  destroyed.  As  all  the  mammalian  lower 
jaws  found,  in  England,  in  the  Jurassic  strata  of  Stonesfield 
and  Purbeck,  exhibit  this  peculiar  process  characteristic  of 
the  Pouched  Animals  (Marsupialia),  we  may  infer,  from 
this  palreontological  fact,  that  they  belonged  to  Marsupials. 
No  Placental  Animals  appear  to  have  existed  during  the 
Mesolithic  Epoch.  At  least  no  fossil  remains,  undoubtedly 
belonging  to  these  and  dating  from  that  epoch,  are  known. 

The  extant  Pouched  Animals,  the  most  generally  known 
of  which  are  the  gramnivorous  Kangaroos  and  the  carni- 
vorous Pouched  Rats,  display  very  considerable  difference  in 
their  organization,  in  the  form  of  their  bodies  and  in  size, 
and  in  many  respects  correspond  to  the  several  orders  of 
Placental  Animals.  The  great  majority  of  them  live  in 
Australia,  in  New  Holland,  and  in  a  few  of  the  Australian 
and  South  Asiatic  islands ;  some  few  species  occur  in 
America.  On  the  other  hand,  there  is  no  longer  a  single 
indigenous  Pouched  Animal  on  the  continents  of  Asia,  of 
Africa,  or  of  Europe.  The  case  was  very  different  during  the 
Mesolithic,  and  also  during  the  earlier  Crenolithic  Epochs. 


EXTANT  POUCHED  ANIMALS.  I  5  I 

The  Neptunian  deposits  of  these  epochs  in  all  quarters  of 
the  globe,  and  even  in  Europe,  contain  abundant  marsupial 
remains  in  great  variety,  some  of  them  being  of  very  large 
size.  From  this  we  may  infer  that  the  extant  Pouched 
Animals  are  but  the  last  remnant  of  a  group  which  was 
once  much  more  widely  developed,  and.  which  was  dis- 
tributed over  the  whole  surface  of  the  globe.  During  the 
Tertiary  Period,  these  succumbed  in  the  struggle  for  life 
with  the  stronger  Placental  Animals,  and  the  survivors  were 
gradually  driven  back  by  the  latter  into  their  present 
restricted  area. 

From  the  Comparative  Anatomy  of  the  extant  Pouched 
Animals,  very  important  conclusions  may  be  drawn  as  to 
their  phylogenetic  intermediate  position  between  Cloacal 
Animals  and  Placental  Animals.  The  incomplete  develop- 
ment of  the  brain,  especially  of  the  fore-brain  (cerebrum), 
the  possession  of  marsupial  bones  (ossa  marsupialia),  the 
simple  structure  of  the  allantois  (which  does  not  as  yet 
develop  a  placenta),  with  many  other  characters,  have  been 
inherited  by  the  Pouched  Animals  from  Cloacal  Animals. 
On  the  other  hand,  they  have  lost  the  independent  coracoid 
bone  (os  coracoideam)  attached  to  the  shoulder  girdle.  A 
more  important  step  consists  in  the  fact  that  a  cloaca  is  no 
longer  formed ;  the  cavity  of  the  rectum,  together  with  the 
anal  opening,  is  separated  by  a  partition  wall  from  the  urinary 
anil  sexual  opening  (sinus  urogenitalis).  Moreover,  all 
Pouched  Animals  develop  special  nipples  on  the  milk-glands, 
which  are  sucked  by  the  young  after  birth.  These  nipples 
project  into  the  cavity  of  a  pouch,  or  marsupium,  in  the 
ventral  side  of  the  mother.  This  pouch  is  supported  by 
a  couple  of  marsupial  bones.  In  it  the  young,  which  are 
30 


152 


THE    EVOLUTION    OF   MAN. 


born  in  a  very  imperfect  condition,  are  carried  by  the 
mother  for  a  long  time ;  until,  in  fact,  they  are  completely 
developed  (Fig.  197).     In  the  large  Giant  Kangaroo,  which 


Fig.  197. — The   Crab-eating  Pouched  Rat   (Philander  cancrivorus).      A 
female  with  two  young  in  its  pouch.     (After  Brehm.) 


THE  POUCHED  ANIMALS  AS  ANCESTORS  OF  MAN.   1 53 

attains  the  height  of  a  man,  the  embryo  develops  in  the 
uterus  but  for  a  month ;  it  is  then  born  in  a  very  incomplete 
condition,  and  attains  all  its  further  development  in  the 
mother's  pouch,  where,  for  about  nine  months,  it  remains 
attached  to  the  milk-glands. 

All  these  and  other  characters  ^especially  the  peculiar 
structure  of  the  internal  and  external  sexual  organs  of  the 
male  and  female)  clearly  show  that  the  whole  sub-class  of 
the  Pouched  Animals  (Marsupialia)  are  a  single  group, 
which  originated  from  the  promammalian  branch.  From  a 
branch  of  these  Pouched  Animals  (perhaps  from  several 
branches)  the  parent-forms  of  the  higher  Mammals,  the 
Placental  Animals,  afterwards  sprang.  Hence  we  must 
reckon  a  whole  series  of  Pouched  Animals  among  the  an- 
cestors of  the  human  race ;  and  these  constitute  the  seven- 
teenth stage  in  the  human  pedigree.158 

The  remaining  stages  of  our  ancestral  line,  from  the 
eighteenth  to  the  twenty-second,  all  belong  to  the  group  of 
Placental  Animals  (Placentalia).  This  very  highly  de- 
veloped group  of  Mammals,  the  third  and  last,  came  into 
the  world  at  a  considerably  later  period.  No  single  known 
fossil,  belonging  to  any  portion  of  the  Secondary  or  Meso- 
lithic  Epoch,  can  be  referred  with  certainty  to  a  Placental 
Animal,  while  we  have  plenty  of  placental  fossils  dating 
from  every  part  of  the  Tertiary  or  Camolithic  Epoch.  From 
this  palreontological  fact  we  may  provisionally  infer  that  the 
third  and  last  main  division  of  Mammals  did  not  develop 
from  the  Pouched  Animals  until  the  beginning  of  the 
Camolithic  Epoch,  or,  at  the  earliest,  till  the  close  of  the 
Mesolithic  Epoch  (during  the  Chalk  Period).  In  our  survey 
of  geological  formations  and  periods  (pp.  12,  19)  we  found 


154  THE   EVOLUTION   OF  MAN. 

how  comparatively  short  this  whole  Tertiary  or  Csenolithic 
Epoch  was.  Judging  from  the  relative  thicknesses  of  the 
various  strata-formations  we  were  able  to  say  that  this 
whole  period,  during  which  Placental  Animals  first  appeared, 
and  assumed  their  respective  forms,  amounted  at  most  to 
about  three  per  cent,  of  the  entire  duration  of  the  organic 
history  of  the  earth.     (Cf.  p.  18.) 

All  Placental  Animals  are  distinguished  from  the  two 
lower  Mammalian  groups  already  considered,  from  the 
Cloacal  Animals  and  Pouched  Animals,  by  many  prominent 
peculiarities.  All  these  characters  are  present  in  Man ;  a 
most  significant  fact.  For  on  the  most  accurate  comparative 
anatomical  and  ontogenetical  researches,  we  may  base  the 
irrefutable  proposition  that  Man  is  in  every  respect  a  true 
Placental  Animal ;  in  him  are  present  all  those  peculiarities 
in  the  structure  and  in  the  development  of  the  body  which 
distinguish  Placental  Animals  from  the  lower  Mammalian 
groups,  and  at  the  same  time  from  all  other  animals. 
Among  these  characteristic  peculiarities  the  higher  develop- 
ment of  the  brain,  the  organ  of  the  mind,  is  especially 
prominent.  The  fore-brain,  or  large  brain  (cerebrum)  is 
much  more  highly  developed  in  these  than  in  lower 
animals.  The  body  {corpus  callosum),  which,  like  a  bridge, 
connects  the  two  hemispheres  of  the  fore-brain,  attains  its 
full  development  only  in  Placental  Animals ;  in  the  Pouched 
Animals  and  Cloacal  Animals  it  exists  merely  as  an  insigni- 
ficant rudiment.  It  is  true  that  in  their  brain  structure 
the  lowest  of  the  Placental  Animals  yet  resemble  Pouched 
Animals  very  nearly ;  but  within  the  Placental  group  Ave 
can  trace  a  continuous  series  of  progressive  stages  in  the 
development  of  the  brain,  ascending  quite  gradually  from 


PLACENTAL   ANIMALS.  1 55 

the  lowest  stage  to  the  very  highly  developed  mind-organ 
of  the  Monkey  and  of  Man.  (Gf.  Chapter  XX.)  The 
human  mind  is  but  a  more  highly  developed  ape-mind. 

The  milk-glands  of  Placental  Animals,  as  of  Marsu- 
pials, are  provided  with  developed  nipples;  but  the  pouch 
in  which  the  immature  young  of  the  latter  are  carried 
about  and  suckled  is  never  present  in  the  former.  Nor  are 
the  marsupial  bones  (ossa  marsupialia)  present  in  Pla- 
cental Animals  ;  these  bones,  which  are  embedded  in  the 
abdominal  wall,  and  rest  on  the  anterior  edge  of  the  pelvis, 
are  common  to  Pouched  Animals  and  Cloacal  Animals,  ori- 
ginating from  a  partial  ossification  of  the  tendons  of  the 
inner  oblique  muscle  of  the  abdomen.  It  is  only  in  a  few 
beasts  of  prey  that  insignificant  rudiments  of  these  bones  are 
found.  The  hook-shaped  process  of  the  lower  jaw,  which 
characterizes  Pouched  Animals,  is  also  entirely  wanting  in 
Placental  Animals. 

The  character,  however,  which  especially  distinguishes 
Placental  Animals,  and  which  has  justly  given  its  name  to 
the  entire  sub-class,  is  the  development  of  the  placenta,  or 
vascular  cake.  We  have  already  spoken  of  this  organ,  in 
describing  the  development  of  the  allantois  in  the  human 
embryo  (vol.  i.  p.  3S2).  The  urinary  sac  or  allantois,  that 
peculiar  bladder  which  grows  out  of  the  posterior  portion  of 
the  intestinal  canal,  is,  we  found,  formed  at  an  early  stage  in 
the  human  embryo  just  as  in  the  germs  of  all  other  Amnion 
Animals.  (Cf.  Figs.  132-135,  vol.  i.  p.  377-380.)  The  thin  wall 
of  this  sac  consists  of  the  same  two  layers,  or  skins,  as  the 
wall  of  the  intestine  itself ;  internally  of  the  intestinal-glan- 
dular layer,  and  externally  of  the  intestinal-fibrous  layer. 
The  cavity  of  the  allantois  is  filled  with  fluid  ;  this  primi- 


156  THE   EVOLUTION   OF   MAN. 

tive  urine  must  be  chiefly  the  product  of  the  primitive 
kidneys.  The  intestinal  fibrous  layer  of  the  allantois  is 
traversed  by  large  blood-vessels  which  accomplish  the  nutri- 
ment and,  especially,  the  respiration  of  the  embryo ;  these 
are  the  navel-vessels,  or  umbilical  vessels  (vol.  i.  p.  400).  In 
all  Reptiles  and  Birds  the  allantois  becomes  an  immense 
sac,  which  encloses  the  embryo  with  the  amnion,  and  which 
does  not  coalesce  with  the  outer  covering  of  the  egg 
(chorion).  InCloacal  Animals  (Monotremata)  and  Pouched 
Animals  (Marsupialia)  the  allantois  is  also  of  this  nature. 
It  is  only  in  Placental  Animals  that  the  allantois  develops 
into  that  very  peculiar  and  remarkable  formation,  called 
the  'placenta,  or  "vascular  cake."  The  nature  of  the  placenta 
is  this :  the  branches  of  the  blood-vessels  which  traverse  the 
wall  of  the  allantois,  penetrate  into  the  hollow  tufts  of  the 
chorion,  which  are  inserted  into  corresponding  depressions 
in  the  mucous  membrane  of  the  maternal  uterus.  As  this 
mucous  membrane  is  also  abundantly  supplied  with  blood- 
vessels, which  conduct  the  mother's  blood  into  the  uterus, 
and  as  the  partition  between  these  maternal  blood-vessels 
and  the  embryonic  vessels  in  the  chorion-tufts  soon  becomes 
extremely  thin,  a  direct  exchange  of  substance  is  soon  de- 
veloped between  the  two  sets  of  blood-vessels,  which  is  of 
the  utmost  importance  for  the  nutrition  of  the  young 
Mammal.  The  maternal  blood-vessels  do  not,  however, 
pass  directly  (anastomosis)  into  the  blood-vessels  of  the 
embryonic  chorion-tufts,  so  that  the  two  kinds  of  blood 
simply  mix,  but  the  partition  between  the  two  sets  of 
vessels  becomes  so  thin,  that  it  permits  the  passage  of  the 
most  important  food-materials,  freed  from  unnecessary 
matter  (transudation,  or  diosmosis).     The  larger  the  embryo 


THE   PLACENTA.  I  57 

grows  in  Placental  Animals,  and  the  longer  it  remains  in 
the  maternal  uterus,  the  more  necessary  does  it  become  that 
special  structural  arrangements  should  meet  the  increased 
consumption  of  food.  In  this  point  there  is  a  very  striking 
difference  between  the  lower  and  the  higher  Mammals.  .In 
Cloacal  Animals  and  Pouched  Animals,  in  which  the  embryo 
remains  for  a  comparatively  brief  time  in  the  uterus,  and  is 
born  in  a  very  immature  condition,  the  circulation  as  it  exists 
in  the  yelk-sac  and  in  the  allantois  suffices  for  nutrition,  as 
in  birds  and  reptiles.  In  Placental  Animals,  on  the  contrary, 
in  which  gestation  is  very  protracted,  and  the  embryo 
remains  much  longer  in  the  uterus,  there  attaining  its  full 
development  within  its  investing  membranes,  a  new  ap- 
paratus is  required  to  convey  a  direct  supply  of  richer 
nutritive  matter ;  and  this  is  admirably  effected  by  the 
development  of  the  placenta. 

In  order  rightly  to  understand  and  appreciate  the  for- 
mation of  this  placenta  and  its  important  modifications  in 
different  Placental  Animals,  we  must  once  more  glance  at  the 
external  coverings  of  the  mammalian  egg.  The  outermost  of 
these  was  originally,  and  during  the  cleavage  of  the  egg 
and  the  first  formation  of  the  axial  portion  of  the  germ, 
formed  by  the  so-called  zona  pellucida,  and  by  the  thick 
albuminous  covering  deposited  externally  on  the  latter 
(Fig.  19,  Fig.  21,  z,  h,  vol.  i.  p.  178). 

We  called  these  two  outer  coverings,  which  afterwards 
amalgamate,  the  prochorion.  This  prochorion  very  soon 
disappears  (in  man  perhaps  in  the  second  week  of  develop- 
ment), and  is  replaced  by  the  permanent  outer  egg-mem- 
brane, the  chorion.  The  latter,  however,  is  simply  the 
serous  membrane,  which,  as  we  have  already  seen,  is  the 


153 


THE    EVOLUTION    OF   MAN. 


product  of  the  outer  germ-layer  of  the  germ-membrane 
vesicle.  (See  vol.i.  p.  401,  and  Fig.  139,  4,  5,  sh,  p.  385.)  This 
is  at  first  a  very  smooth,  thin  membrane,  surrounding  the 
entire  egg,  as  a  closed  spherical  vesicle,  and  consisting  of  a 
single  layer  of  exoderm  cells.  The  chorion,  however,  be- 
comes very  soon  studded  with  a  number  of  little  protuber- 
ances or  tufts  (Fig.  139,  5,  chz).  These  fit  themselves  into 
indentations  in  the  mucous  membrane  of  the  uterus,  and 
thus  secure  the  egg  to  the  wall  of  the  latter.  The  tufts 
are,  however,  not  solid,  but  hollow,  like  the  fingers  of  a 
glove.  Like  the  whole  chorion,  these  hollow  tufts  consist  of 
a  thin  layer  of  cells  belonging  to  the  horn-plate.  They 
very  soon  attain  an  extraordinary  development,  growing 
and  branching  rapidly.     In  the  spaces  between  them,  new 

Frc.  198.— Egg-coverings  of 
the  human  embryo  (diagram- 
matic) :  to,  the  thick  fleshy  wall 
of  the  uterus ;  plu,  placenta, 
the  inner  stratum  (plu')  of 
which  has  extended  processes 
between  the  chorion-tufts  (chz) 
(chf,  tufted,  chl,  smooth  cho- 
rion) ;  a,  amnion  ;  ah,  amnion 
cavity ;  as,  amnion  sheath  of 
the  navel-cord  (passing  down 
into  the  navel  of  the  embryo, 
which  is  not  rejjresented  here)  ; 
dg,  yelk-duct ;  ds,  yelk-sac ; 
dv,  dr,  decidua  (dv,  true,  dr, 
false).  The  uterus-cavity  (uh) 
opens  below  into  the  vagina, 
above,  on  the  right  hand  side, 
into  an  oviduct  (t).  (After 
Kolliker.) 

tufts  arise  in  all  directions  from  the  serous  membrane,  and 
thus  before  long  (in  the  human  embryo  in  the  third  week) 


DEVELOPMENT  OF  THE  PLACENTA.         I  59 


the  whole  outer  surface  of  the  egg  is  covered  with  a  dense 
forest  of  tufts  (Fig.  134). 

These  hollow  tufts  are  now  penetrated  from  within  by 
the  branching  blood-vessels,  which  originate  from  the  in- 
testinal fibrous  layer  of  the  allantois,  and  which  contain 
the  blood  of  the  embryo,  introduced  through  the  navel  vessels 
(Fig.  198,  chz).  On  the  other  hand,  dense  networks  of 
blood-vessels  develop  in  the  mucous  membrane,  which 
lines  the  inner  surface  of  the  uterus,  particularly  in  the 
neighbourhood  of  the  depressions  into  which  the  chorion- 
tufts  penetrate  (phi).  These  vascular  networks  receive  the 
blood  of  the  mother  introduced  through  the  uterus  vessels. 
The  whole  mass  of  these  two  sets  of  vessels,  which  are  here 
most  intimately  connected,  together  with  the  connecting 
and  enveloping  tissues,  is  called  the  placenta,  or  "  vascular 
cake."  Properly  speaking,  the  placenta  consists  of  two 
quite  different,  though  closely  connected,  parts  ;  internally, 
of  the  embryonic  placenta  (placenta  fcetalis,  Fig.  198,  chz), 
and  externally  of  the  maternal  placenta  ('placenta  uterina, 
Fig.  198,  plu).  The  latter  is  formed  by  the  uterine  mucous 
membrane  and  its  blood  vessels :  the  former  by  the 
secondary  chorion  and  the  navel  vessels  of  the  embryo. 

The  mode  in  which  these  two  "  vascular  cakes "  com- 
bine to  form  the  placenta,  as  well  as  the  structure,  form, 
and  size  of  the  latter,  differs  much  in  different  Placental 
Animals,  and  affords  valuable  data  for  natural  classification, 
and  hence  also  for  the  tribal  history  of  the  whole  sub-class. 
The  latter  is  primarily  divisible  into  two  main  divisions, 
based  on  these  differences  :  the  lower  Placental  Animals, 
which  are  called  Indecidua,  and  the  higher  Placental 
Animals,  or  Deciduata. 


l60  THE   EVOLUTION   OF   MAN. 

To  the  Indecidua,  or  lower  Placental  Animals,  belong 
two  very  comprehensive  and  important  vertebrate  groups  : 
(1)  the  Hoofed  Animals  (Ungulata) — the  Tapirs,  Horses, 
Swine,  Ruminants,  and  others ;  (2)  the  Whale-like  animals 
(Cetomorpha) — the  Sea-cows,  Porpoises,  Dolphins,  Whales, 
and  others.  In  all  these  Indecidua  the  chorion  tufts  are 
distributed,  singly  or  in  bunches,  over  the  entire  surface  of 
the  chorion,  or  over  the  greater  part  of  it.  They  are  but  very 
loosely  attached  to  the  mucous  membrane  of  the  uterus,  so 
that  the  entire  outer  egg-membrane  with  its  tufts  might 
easily  and  without  using  force  be  drawn  out  of  the  depressions 
in  the  uterine  mucous  membrane,  just  as  the  hand  is  with- 
drawn from  a  glove.  The  two  "  vascular  cakes "  do  not 
really  coalesce  at  any  point  of  their  contact.  Hence,  at 
birth  the  "embryonic  cake"  {placenta  fcetalis)  is  alone 
removed  ;  the  "  maternal  cake  "  {placenta  uterina)  is  not 
displaced.  The  entire  mucous  membrane  of  the  gravid 
uterus  is  but  little  altered,  and,  at  parturition,  suffers  no 
direct  loss  of  substance. 

The  structure  of  the  placenta  in  the  second  and  higher 
division  of  Placental  Animals,  the  Deciduata,  is  very  dif- 
ferent. To  this  comprehensive  and  very  highly  developed 
mammalian  group  belong  all  Beasts  of  Prey  and  all  Insect- 
eaters,  Gnawers  (Rodent la),  Elephants,  Bats,  Semi-apes,  and, 
lastly,  Apes  and  Man.  In  all  these  Deciduata  the  whole 
surface  of  the  chorion  is  also  at  first  thickly  covered  with 
tufts.  These,  however,  afterwards  disappear  from  part  of 
the  surface,  while  they  develop  all  the  more  vigorously  in 
the  remainder.  The  smooth  chorion  (chorion  Imve,  Fig.  198, 
chl)  thus  becomes  distinct  from  the  tufted  chorion  (chorion 
frondosum,  Fig.  198,  chf).     On  the  former  there  are  only 


INDECIDUA   AND   DECIDUA.  l6l 

minute  and  scattered  tufts,  or  none  at  all;  while  the  latter 
is  thickly  overgrown  with  highly  developed  and  large  tufts. 
In  the  Deciduata  the  tufted  chorion  alone  forms  the 
placenta. 

Yet  more  characteristic  of  the  Deciduata  is  the  very 
peculiar  and  intimate  connection  which  is  developed  in 
these  between  the  tufted  chorion  and  the  contiguous 
portion  of  the  uterine  mucous  membrane,  and  which  must 
be  regarded  as  a  true  coalescence.  The  vascular  tufts  of 
the  chorion  push  their  branches  into  the  sanguineous  tissue 
of  this  mucous  membrane  in  such  a  way,  and  the  two  sets 
of  vessels  are  in  such  close  contact  and  are  so  interlaced, 
that  the  embryonic  placenta  is  no  longer  distinguishable 
from  the  maternal  placenta ;  the  two  form  one  whole — a 
compact  and  apparently  simple  placenta.  Owing  to  this 
intimate  coalescence,  a  portion  of  the  uterine  mucous  mem- 
brane of  the  mother  comes  away,  at  birth,  with  the  firmly 
adherent  egg-membrane.  The  portion  of  the  mother's  body 
which  is  thus  removed  in  parturition  is  called,  on  account 
of  its  separable  nature,  the  deciduous  membrane  (decidua). 
Ail  Placental  Animals  which  possess  this  deciduous  mem- 
brane are  classed  together  as  Deciduata.  The  removal  of 
this  membrane  at  parturition,  of  course,  causes  a  greater  or 
less  loss  of  blood  by  the  mother,  which  does  not  occur  in 
the  Indecidua.  In  the  Deciduata,  moreover,  the  lost  portion 
of  the  uterine  mucous  membrane  must  be  replaced,  after 
parturition,  by  a  renewal  of  the  tissue. 

The  structure  of  the  placenta  and  deciduous  membrane 
is,  however,  by  no  means  identical  throughout  the  compre- 
hensive group  of  Deciduata.  On  the  contrary,  there  are 
many  important   differences  in    this  respect,  which  are  in 


1 62  THE   EVOLUTION   OF   MAN. 

some  degree  connected  with  other  important  structural 
characters  {e.g.,  the  structure  of  the  brain,  of  the  teeth,  ot  the 
feet),  and  which  may  justly,  therefore,  be  turned  to  account 
in  the  phylogenetic  classification  of  Placentals.  In  the  first 
place,  two  great  groups  of  Deciduata  may  be  distinguished 
according  to  the  form  of  the  placenta :  in  the  one  group  it 
is  ring-shaped  or  girdle-shaped;  in  the  other  it  is  discoid  or 
cake-shaped.  In  Deciduata  with  girdle-shaped  placenta 
(Zonoplacentalia)  the  poles  of  the  oval  egg  take  no  part 
in  the  formation  of  the  placenta.  The  "vascular  cake" 
resembles  a  broad  ring-like  girdle,  embracing  the  central 
zone  of  the  egg.  It  is  so  in  Beasts  of  Prey  (Camassia), 
both  in  the  terrestrial  forms  (Camivora)  and  in  the  marine 
forms  (Plnnipedia).  A  similar  girdle-shaped  placenta  is 
found  in  the  False-hoofed  Animals  (Chelojphora) :  the 
elephants,  and  Klip  Das  (Hyrax)  with  its  allies,  which  were 
formerly  classed  as  Hoofed  Animals.  All  these  Zonoplacen- 
talia belong  to  one  or  more  side-branches  of  the  Deciduata, 
which  are  not  nearly  allied  to  Man. 

The  second  and  most  highly  developed  group  is  formed 
by  the  Deciduata  with  discoidal  placenta  (Disco placentalia). 
The  formation  of  the  placenta  is  here  most  localized  and 
its  structure  most  fully  developed.  The  placenta  forms  a 
thick,  spongy  cake,  usually  in  the  form  of  a  circular  or 
oval  disc,  and  attached  only  to  one  side  of  the  uterine 
wall.  The  greater  part  of  the  embryonic  egg-membrane  is, 
therefore,  smooth,  without  developed  tufts.  To  the  Disco- 
placentalia  belong  the  Semi-apes  and  Insect-eaters,  the 
Diggers  (Effoclienta)  and  the  Sloths,  Rodents  and  Bats, 
Apes  and  Man.  Comparative  Anatomy  enables  us  to  infer 
that  of  these  various  orders  the  Semi-apes  are  the  parent- 


SEMI- APES.  163 

group  from  which  all  other  Discoplacentals,  and  perhaps 
even  all  Deciduous  Animals,  have  developed  as  divergent 
branches.     (Cf.  Tables  XXIII.  and  XXIV.) 

The  Semi-apes  (Prosimice)  are  now  represented  only  by- 
very  few  forms.  These,  however,  are  very  interesting,  and 
must  be  regarded  as  the  last  remnants  of  a  group  once  rich 
in  forms.  This  group  is  certainly  very  ancient,  and  was 
probably  very  prominent  during  the  Eocene  Epoch,  Their 
present  degraded  descendants  are  scattered  widely  over  the 
southern  portion  of  the  Old  World.  Most  of  the  species 
inhabit  Madagascar ;  a  few  the  Sunda  Islands  ;  a  few  others 
the  continents  of  Asia  and  Africa.  No  living  or  fossil  Semi- 
apes  have,  as  yet,  been  found  in  Europe,  America,  or  Aus- 
tralia.159 The  widely  scattered  posterity  of  the  Semi-apes 
is  considerably  diversified.  Some  forms  seem  nearly  allied 
to  the  Marsupials,  especially  to  the  Pouched-rats.  Others 
(Macrotarsi)  are  very  near  akin  to  the  Insect-eaters,  and 
yet  others  (Cheiromys)  to  the  Gnawers  {Rodentia).  One 
genus  (Galeopithecus)  forms  a  direct  transition  to  the  Bats. 
Finally,  some  of  the  Semi-apes  (Brachytarsi)  approach  very 
near  to  true  Apes.  Among  the  latter  are  some  tail-less  forms 
{e.g.,  the  Lori,  Stenops,  Fig.  199).  From  these  highly  in- 
teresting and  important  relations  of  the  Semi-apes  to  the 
various  Discoplacental  orders,  we  may  fairly  infer  that 
of  the  extant  representatives  of  this  group,  they  are  the 
nearest  to  the  common  primitive  parent-form.  Among  the 
direct  common  ancestors  of  Apes  and  Men,  there  must  have 
been  some  Deciduata  which  we  should  class  anions  the 
Semi-apes,  were  we  to  see  them  alive.  We  may  therefoi'e 
consider  this  order  as  a  special  stage,  following  the  Pouched 
Animals,  as  the  eighteenth  stage  in  the  human  pedigree. 


164 


THE   EVOLUTION    OF   MAN. 


Probably  our  ancestors  among   the    Semi-apes   closely    re- 
sembled the  extant  Brachytarsi  or  Lemurs  {Lemur,  Lichan- 


Fig.  199. — The  Slender  Lori  of  Ceylon  (Stenops  gracilis). 

otus,  Stenops),  and,  like  these,  led  a  quiet  life,  climbing  on 
trees.  The  extant  Semi-apes  are  mostly  nocturnal  animals 
of  gentle  and  melancholy  disposition,  subsisting  on  fruits. 


APES.  165 

The  Semi-apes  are  immediately  followed  by  the  true 
Apes  (Simice),  as  the  nineteenth  stage  in  the  human  pedi- 
gree. It  has  long  been  beyond  doubt  that  of  all  animals 
the  Apes  are  in  all  respects  the  most  nearly  allied  to  Man. 
Just  as,  on  the  one  side,  the  lowest  Apes  approach  very  near 
to  the  Semi-apes,  so,  on  the  other  side,  do  the  highest  Apes 
most  closely  resemble  Man.  By  carefully  studying  the  Com- 
parative Anatomy  of  Apes  and  Man,  it  is  possible  to  trace  a 
gradual,  uninterrupted  advance  in  the  Ape-organization  up  to 
the  purely  human  structure;  and  on  impartially  testing  this 
"Ape-question,"  which  has  lately  been  agitated  with  such 
passionate  interest,  we  shall  infallibly  have  to  acknowledge 
the  important  fact,  which  was  first  explicitly  laid  down  by 
Huxley,  that  "  whatever  system  of  organs  be  studied,  the 
comparison  of  their  modifications  in  the  ape  series  leads  to 
one  and  the  same  result — that  the  structural  differences 
which  separate  Man  from  the  Gorilla  and  Chimpanzee  are 
not  so  great  as  those  which  separate  the  Gorilla  from  the 
lower  Apes."  In  phylogenetic  language  this  pregnant  law 
established  in  so  masterly  a  manner  by  Huxley,  is  equiva- 
lent to  the  popular  phrase  :  Man  is  descended  from  the  Ape. 

In  order  to  become  convinced  of  the  truth  of  this  law, 
let  us  now  once  more  consider  the  placenta  and  deciduous 
membrane,  on  the  varied  structure  of  which  we  justly  laid 
special  stress.  Men  and  Apes,  in  the  structure  of  their  disc- 
shaped placenta  and  in  their  decidua,  do,  indeed,  coincide 
on  the  whole  with  all  other  Discoplacental  Animals.  But 
in  the  more  delicate  structure  of  these  parts  Man  is  dis- 
tinguished by  peculiarities  which  he  shares  only  with  Apes, 
and  which  are  absent  in  other  Deciduata.  Thus  in  Man 
and  in   the  Apes  three  distinct  parts  are  recognized  in  the 


1 66 


THE   EVOLUTION    OF  MAN. 


deciduous  membrane ;  these  parts  may  be  called  the  outer, 
the  inner,  and  the  placental  deciduous  membrane.  The 
outer  or  true  membrane  (d.  externa  or  vera,  Fig.  198,  dv, 
Fig.  200,  g),  is  that  portion  of  the  uterine  mucous  membrane 
which  coats  the  internal  surface  of  the  uterus  wherever  the 

K  msaL    r 


Fig.  200. — Human  embryo,  twelve  weeks  old,  with  its  coverings;  natural 
size.  The  navel  cord  passes  from  the  navel  to  the  placenta  :  b,  amnion ; 
c,  chorion  ;  d,  placenta  ;  d',  remains  of  tufts  on  the  smooth  chorion  ;  /,  de- 
cidua  reflexa  (inner)  ;    g,  decidua  vera  (outer).     (After  Bernhard  Schultze.) 

latter  is  not  attached  to  the  placenta.  The  placental  or 
spongy  deciduous  membrane  (d.  placentalis  or  serotina, 
Fig.  198,  plu,  Fig.  200,  d)  is  simply  the  maternal  placenta 


THE   DECIDUOUS   MEMBRANE   IN    MAN   AND   APES.        1 67 

itself,  or  the  maternal  part  of  the  "  vascular  cake  "  (pla- 
centa utcrina),  i.e.,  that  part  of  the  uterine  mucous  mem- 
brane which  coalesces  intimately  with  the  chorion-tufts  of 


Fig.  201. — Mature  human  embryo  (at  the  end  of  pregnancy),  in  its  natural 
position,  taken  out  of  the  uterus.  On  the  inner  surface  of  the  latter  (on 
the  left)  is  the  placenta,  which  is  attached  to  the  navel  of  the  child  by  the 
navel  cord.     (After  Bernhard  Schultze.) 

the  embryonic  placenta  (placenta  fcetalis).  Lastly,  the 
inner  or  false  deciduous  membrane  (d.  interna  or  reflexa, 
Fig.  198,  ch;  Fig.  200,  /)  is  that  portion  of  the  uterine  mucous 
membrane  which,  as  a  peculiar  thin  envelope,  covers  all  the 
rest  of  the  egg-surface,  lying  immediately  over  the  tuftless 
smooth  chorion  (chorion  have).  The  origin  of  these  three 
distinct  deciduous  membranes,  concerning  which  erroneous 
notions  have  been  entertained  (still  retained  in  the  nomen- 
clature), is  plain  enough ;    the  external  or  true  deciduous 


1 68  THE   EVOLUTION   OF   MAN. 

membrane  is  a  peculiar  modification,  afterwards  lost,  of  the 
superficial  layer  of  the  original  mucous  membrane  of  the 
uterus.  The  placental  membrane  is  that  portion  of  the 
preceding  which  is  completely  modified  by  the  intrusion  of 
the  chorion-tufts  and  is  employed  in  forming  the  placenta. 
Lastly,  the  inner  deciduous  membrane  is  formed  by  a 
ring-shaped  fold  of  the  mucous  membrane  (at  the  point 
of  union  of  the  d.  vera  and  the  d.  serotina)  which  rises, 
orows  round  the  egg,  and  closes  in  the  same  way  as  the 
amnion.160 

The  peculiar  anatomical  characters  which  mark  the  human 
egg-membrane  re-occur,  in  the  same  form,  only  in  Apes.  All 
other  Discoplacental  Animals  present  greater  or  less  differ- 
ences in  these  points,  the  conditions  being  generally  more 
simple.  This  is  the  case,  for  instance,  in  the  structure  of 
the  placenta  itself,  in  the  coalescence  of  the  chorion  tufts 
with  the  decidua  serotina.  The  matured  human  placenta 
is  a  circular  (rarely  oval)  disc  of  a  soft,  spongy  character, 
6  to  8  inches  in  diameter,  about  1  inch  thick,  and  weighing 
from  1  to  1|  lb.  Its  convex,  external  surface  (that  which 
coalesces  with  the  uterus)  is  very  uneven,  and  tufted.  Its 
internal,  concave  surface  (that  which  is  turned  towards  the 
cavity  of  the  egg)  is  quite  smooth,  and  clothed  by  the  amnion 
(Fig.  198,  a).  From  near  the  centre  of  the  placenta  springs 
the  navel  cord  (funiculus  umbilicalis),  the  development 
of  which  we  have  already  observed  (vol.  i.  p.  383).  It  also  is 
coated  by  the  amnion  as  with  a  sheath,  which  at  the  navel 
end  passes  directly  into  the  abdominal  skin  (Fig.  200,  201). 
The  mature  navel  cord  is  a  cylindrical  cord,  coiled  spirally 
around  its  axis,  and  usually  about  20  inches  long  and  |-  inch 
thick.     It  consists  of  gelatinous  connective  tissues  ("  Whar- 


THE   HUMAN   PLACENTA.  1 69 

ton's  jelly  "),  in  which  are  contained  the  remnants  of  the 
yelk-vessels  and  of  the  great  navel  vessels ;  the  two  navel 
arteries  which  convey  the  blood  of  the  embryo  to  the  pla- 
centa, and  the  great  navel  vein  which  brings  back  the  blood 
from  the  latter  to  the  heart.  The  numerous  fine  branches 
of  these  embryonic  navel  vessels  pass  into  the  branched 
chorion  tufts  of  the  foetal  placenta,  and  with  these,  finally, 
grow,  in  a  very  peculiar  way,  into  large  blood-filled  cavities, 
which  spread  themselves  in  the  uterine  placenta  and  con- 
tain blood  from  the  mother.  The  anatomical  relations,  very 
complex  and  difficult  to  comprehend,  which  are  developed 
between  the  embryonic  and  the  maternal  placenta,  exist  in 
this  form  only  in  Man  and  in  the  higher  Apes,  while  in  all 
other  Deciduous  Animals  their  form  is  more  or  less  different. 
The  navel  cord,  also,  is  proportionately  longer  in  Man  and 
in  Apes  than  in  other  Mammals. 

As  in  these  important  characters,  so  also  in  every  other 
morphological  respect,  Man  appears  as  a  member  of  the 
order  of  Apes,  and  cannot  be  separated  from  the  latter.  The 
great  originator  of  systematic  description  of  nature,  Karl 
Linnaeus,  with  prophetic  penetration,  united  Men,  Apes, 
Semi-apes,  and  Bats  in  a  single  natural  division,  under  the 
name  of  Primates,  that  is,  the  first,  the  lords  of  the  animal 
kingdom.  Later  naturalists  dissolved  this  order  of  Primates. 
The  Gottingcn  anatomist,  Blumenbach,  first  placed  Man  in 
a  special  order,  which  he  called  that  of  Two-handed  Animals 
(Bimana) :  in  a  second  order,  he  united  Apes  and  Semi- 
apes  under  the  name  of  Four-handed  Animals  (Quad- 
rumana),  while  a  third  order  included  the  distantly  related 
Bats  (Chiroptera).  The  separation  of  the  Bimana  and 
Quadrumana  was  retained  by  Cuvier  and  most  succeeding 


170  THE   EVOLUTION   OF   MAN. 

zoologists.  It  seems  very  important,  but  is  really  wholly 
unjustifiable.  This  was  first  shown  in  the  year  1SG3  by 
Huxley.  Supported  by  very  accurate  Comparative  Anato- 
mical researches' he  proved  that  Apes  are  as  "two-handed" 
as  Men,  or,  conversely,  that  Men  are  as  "  four-handed  "  as 
Apes.  Huxley  showed,  with  convincing  clearness,  that  the 
ideas  previously  held  of  the  hand  and  the  foot  were  false, 
and  were  incorrectly  founded  on  physiological  instead  of  on 
morphological  distinctions.  The  circumstance  that  in  the 
hand,  the  thumb  may  be  opposed  to  the  other  four  fingers, 
thus  permitting  the  act  of  grasping,  appeared  especially  to 
distinguish  the  hand  from  the  foot,  in  which  the  correspond- 
ing great  toe  cannot  be  thus  opposed  to  the  four  remaining 
toes.  Apes,  on  the  contrary,  can  grasp  in  this  way  with  the 
hind-foot  as  well  as  with  the  fore-foot,  and  were  therefore 
regarded  as  four-handed.  Many  tribes,  however,  among  the 
lower  races  of  men,  especially  many  negro  tribes,  use  the  foot 
in  the  same  way  as  the  hand.  In  consequence  of  early  habit 
and  continued  practice,  they  are  able  to  grasp  as  well  with 
the  foot  as  with  the  hand  (for  example,  in  climbing,  they 
grasp  the  branches  of  trees).  Even  new-born  children  of  our 
own  race  have  a  very  strong  grasping  power  in  the  great  toe, 
with  which  they  can  hold  a  spoon  as  fast  as  with  the  hand. 
The  physiological  distinction  between  hand  and  foot  can, 
therefore,  neither  be  strictly  carried  out,  nor  scientifically 
established.  Morphological  characters  must  be  used  for  this 
purpose. 

A  sharp  morphological  distinction  of  this  kind — that  is, 
one  founded  on  anatomical  structure — between  hand  and 
foot,  between  the  anterior  and  the  posterior  limbs,  is  actually 
possible.     There   are   essential   and   permanent  differences 


MAN   AND   APE.  171 

both  in  the  structure  of  the  bony  skeleton  and  in  that  of 
the  muscles  which  are  attached  to  the  hand  and  the  foot ; 
and  these  are  exactly  the  same  in  Man  and  in  the  Ape. 
There  is,  for  instance,  an  essential  difference  in  the  arrange- 
ment and  number  of  the  wrist-bones  of  the  hand  (carpus) 
and  the  ankle-bones  of  the  foot  (tarsus).  The  muscle-masses 
present  equally  constant  differences.  The  posterior  ex- 
tremity, the  foot,  has  always  three  muscles  (a  short  flexor 
muscle,  a  short  extensor  muscle,  and  a  long  muscle  attached 
to  the  muscles  of  the  tibia)  which  are  never  present  in 
the  anterior  extremity,  the  hand.  The  disposition  of  the 
muscles  is  also  very  different  in  the  two  sets  of  limbs. 
These  characteristic  differences  between  the  anterior  and 
the  posterior  extremities  occur  in  Man  just  as  in  Apes. 
There  can,  therefore,  be  no  doubt,  that  the  foot  of  the 
Ape  deserves  the  name  as  truly  as  that  of  the  Man ;  and 
that  all  true  Apes  are  as  genuinely  two-handed  animals 
(Bimana)  as  Man.  Thus  the  usual  distinction  of  the  Apes 
as  Quadrumana  is  wholly  unjustifiable. 

It  might  now  be  asked  whether,  quite  apart  from  these, 
there  are  not  other  marks  by  which  Man  is  more  widely 
separated  from  the  Apes  than  are  the  different  species  of 
Apes  from  each  other.  Huxley  has  given  a  final  negative 
to  this  question  so  convincingly,  that  the  opposition  now 
raised  against  him  in  many  quarters  must  be  regarded  as 
completely  unfounded  and  ineffective.  Based  on  an  accurate 
study  of  the  Comparative  Anatomy  of  all  parts  of  the  body, 
Huxley  brought  forward  very  significant  proof  that,  in 
every  anatomical  respect,  the  differences  between  the  highest 
and  the  lowest  Apes  are  greater  than  the  corresponding 
differences  between  the  highest  Apes  and  Man.     He  there- 


172  THE   EVOLUTION   OF   MAN. 

fore  restored  Linnaeus' s  order  of  Primates  (excluding  the 
Bats),  and  divided  it  into  three  different  sub-orders,  the 
first  of  which  is  formed  by  the  Semi-apes  (Lemur ida),  the 
second  by  the  true  Apes  (Simiadcu),  and  the  third  by  Men 
(Anthropidce).161 

Yet,  if  we  proceed  logically  and  without  prejudice,  in 
accordance  with  the  principles  of  scientific  reasoning,  we 
find,  on  the  basis  of  Huxley's  own  law,  this  division  in- 
adequate, and  must  go  considerably  further.  As  I  first 
showed  in  18G6,  in  treating  this  question  in  my  Generelle 
Morpliologie,  we  are  fully  justified  in  taking  at  least  one 
important  step  further,  in  assigning  to  Man  his  natural 
place  in  one  of  the  divisions  of  the  Ape-order.  All  the 
characters  distinctive  of  this  one  division  of  the  Apes  are 
present  in  Man,  while  they  are  absent  in  other  Apes.  We 
are,  therefore,  not  justified  in  forming  a  distinct  order  for 
Man  apart  from  the  true  Apes. 

The  order  of  the  true  Apes  (Shnice),  the  Semi-apes  being 
excluded,  has  long  been  divided  into  two  natural  main 
groups,  which,  among  other  points,  are  distinguished  by 
their  geographical  distribution.  Those  of  one  division 
(Hesperopitheci,  or  Western  Apes)  live  in  the  New  World, 
in  America.  The  other  division,  to  which  Man  belongs,  is 
that  of  the  Heojntheci,  or  Eastern  Apes ;  these  live  in  the 
Old  World,  in  Asia,  Africa,  and,  formerly,  in  Europe.  All 
the  Apes  of  the  Old  World,  all  Heopitheci,  share,  in  common 
with  Man,  all  those  characteristics  to  which  special  promin- 
ence is  justly  given,  in  distinguishing  these  two  groups  of 
Apes,  in  zoological  classification ;  among  these  characteristics 
the  structure  of  the  teeth  is  most  prominent.  The  objec- 
tion is  at  once  evident  that  the  teeth  are,  in  a  physiological 


THE  TEETH.  1 73 

sense,  much  too  subordinate  a  part  of  the  body  to  justify  so 
great  a  weight  being  attached  to  their  structure  in  so  im- 
portant  a  question.  There  are,  however,  good  reasons  for 
this  prominent  consideration  of  the  structure  of  the  teeth ; 
and  it  is  with  perfect  correctness  and  propriety  that  sys- 
tematic zoologists  have,  for  more  than  a  century,  given 
special  weight  to  this  character  in  systematically  dis- 
tinguishing and  arranging  the  mammalian  orders.  The 
number,  form,  and  disposition  of  the  teeth  are  transmitted 
much  more  accurately  within  the  respective  orders  of  the 
mammals  than  are  most  other  zoological  characteristics. 
The  structure  of  the  human  teeth  is  well  known.  In  matu- 
rity there  are  32  teeth  in  our  jaws,  and  of  these  32  teeth, 
8  are  front-teeth,  4  canine-teeth,  and  20  molar-teeth.  The 
eight  front-teeth  or  incisors  (denies  incisivi),  which  are 
situated  in  the  centre  of  the  jaws,  exhibit  characteristic 
differences  in  the  upper  and  lower  jaw.  In  the  upper  the 
inner  incisors  are  larger  than  the  outer;  in  the  lower  jaw, 
on  the  contrary,  the  inner  incisors  are  smaller  than  the 
outer.  Next  to  these,  on  each  side,  both  in  the  upper  and 
lower  jaw,  is  a  corner- tooth,  which  is  larger  than  the  in- 
cisors, the  so-called  eye-tooth,  or  canine  (dens  caninus). 
Sometimes  this  tooth  becomes  very  prominent  in  Men,  as  in 
most  Apes  and  many  other  Mammals,  and  forms  a  sort  of 
tusk.  Finally,  next  to  this,  on  each  side,  and  in  each  jaw, 
are  situated  five  back-teeth,  or  molar- teeth  (dentes  raolares), 
of  which  the  two  foremost  (the  bicuspid  teeth)  are  small, 
have  but  a  single  fang,  and  are  subject  to  the  change  of 
teeth,  while  the  three  hinder  molars  are  much  larger,  have 
two  fangs,  and  do  not  appear  till  after  the  temporaiy  teeth 
have  been  shed  (so-called  "  grinders ").     The  Apes  of  the 


174  THE   EVOLUTION   OF   MAN. 

Old  World  have  exactly  this  human  structure  of  the  teeth, — 
all  Apes  which  have  as  yet  been  found,  either  living  or  as 
fossils,  in  Africa,  Asia,  and  Europe.  All  Apes  of  the  New 
World,  on  the  contrary,  all  American  Apes,  have  an  extra 
tooth  on  both  sides  of  each  jaw ;  this  is  a  biscupid  tooth. 
Thus  they  have  six  back-teeth  on  both  sides  of  each  jaw, — 
in  all,  thirty-six  teeth.  This  characteristic  difference  be- 
tween the  Eastern  and  Western  Apes  has  been  so  constantly 
transmitted  within  the  two  groups,  that  it  is  of  the  greatest 
value  to  us.  A  small  family  of  South  American  Apes  does, 
indeed,  appear  to  form  an  exception  in  this  respect.  The 
pretty  little  Silk  Apes,  or  Marmosets  (Hapalida),  namely,  to 
which  the  Brush-monkey  (Midas)  and  the  tufted  Marmoset 
(Jacchus)  belong,  have  but  five  back-teeth  in  each  half  of 
the  jaw,  instead  of  six,  and,  accordingly,  seem  to  approach 
nearer  the  Eastern  Apes.  But  on  closer  observation  it 
is  found  that,  like  all  the  Western  Apes,  they  have  the 
three  biscupids,  and  that  the  hindmost  grinder  has  been 
lost.  Thus  this  apparent  exception  confirms  the  value  of 
the  distinction. 

Among  the  other  marks  by  which  the  two  main  groups 
of  the  Apes  are  distinguished,  the  structure  of  the  nose  is 
specially  important  and  prominent.  In  all  Old  World  Apes 
the  structure  of  the  nose  is  the  same  as  in  Man ;  namely,  a 
comparatively  narrow  partition  of  the  two  halves,  so  that 
the  nostrils  are  directed  downwards.  In  a  few  Eastern  Apes, 
the  nose  projects  as  prominently  and  is  as  characteristically 
formed  as  in  Man.  We  have  already  called  attention, 
in  this  respect,  to  the  remarkable  Nose-ape  (Semno- 
pithecus  nasicus),  which  has  a  well-curved  and  long  nose 
(Fig.  202).     Most  of  the  Eastern  Apes  have,  it  is  true,  a 


THE   NOSE. 


175 


somewhat  flatter  nose,  as,  for  instance,  has  the  white-nosed 
Sea-cat  (Cercopithecus  petaurista,  Fig.  203) ;  yet  in  all  the 
partition  of  the  nose  is  narrow  and  thin.  On  the  contrary, 
all  American  Apes  have  a  different  nasal  structure.  In 
them,  the  partition  is  peculiarly  broadened  and  thickened 
below,  and  the  wings  of  the  nose  are  not  developed,  in  con- 
sequence of  which  the  nostrils  are  not  below,  but  are 
turned  outwards.  This  characteristic  difference  in  the 
structure  of  the  nose  has  also  been  so   accurately  trans- 


Frc.  202. — ITead  of  Nose-ape  (Semnopithecus  nasicus) . 

Fig.  203. — The  white-nosed  Sea-cat  (Cercopithecus  petaurista). 


mitted  in  both  groups,  that,  on  account  of  it,  the  Apes  of 
the  New  World  have  been  called  Flat-nosed  (Platyrhvnce), 
and  those   of  the  Old  World  Narrow-nosed   (Catarhince). 
The  former  are,  on  the  average,  inferior  in  organization. 
31 


176  THE   EVOLUTION   OF   MAN. 

The  division  of  the  order  of  Apes  into  two  sub-orders, 
the  Platyvliince  and  the  Catarhmce,  is,  on  account  of  the 
constant  hereditary  characters,  now  generally  accepted  by 
zoologists,  and  receives  much  support  from  the  geographical 
distribution  of  the  two  groups  between  the  New  and  Old 
Worlds.  From  this  follows  the  direct  inference,  very  im- 
portant in  its  bearing  on  the  Phylogeny  of  Apes,  that,  from 
the  primaeval  common  parent-form  of  the  Ape-order,  two 
diverging  lines  branched  out  at  a  very  early  period,  one  of 
which  spread  over  the  New  World,  the  other  over  the  Old. 
It  is  certain  that  all  the  Flat-nosed  Apes,  on  the  one  hand, 
are  descendants  of  a  common  parent-form,  and,  on  the  other 
hand,  all  the  Narrow-nosed  Apes  from  another 

An  inference  concerning  our  own  pedigree  may  be  drawn 
from  this.  Man  has  exactly  the  same  characters,  the  same 
peculiar  formation  of  the  teeth  and  nose,  as  all  the 
Catarhince,  and  is  as  thoroughly  distinguished  by  these 
charateristics  from  the  PlatyrhincB.  We  are  therefore  com- 
pelled, in  classifying  the  Primates,  to  assign  to  Man  a  place 
in  the  Narrow-nosed  group.  The  bearing  of  this  on  our 
tribal  history  is,  that  Man  is  immediately  related  in  blood 
to  the  apes  of  the  Old  World,  and  may  be  traced  from  a 
parent-form  common  to  all  other  Catarhinse  also.  Man  is 
a  genuine  Narrow-nosed  Ape  in  his  whole  structure  and 
in  origin,  and  has  descended  from  some  unknown,  extinct 
Catarhine  form  in  the  Old  World.  On  the  other  hand,  the 
Apes  of  the  New  World,  the  Flat-nosed  group,  constitute  a 
diverging  branch  of  our  family  tree,  and  stand  in  no  near 
genealogical  relation  to  the  human  race. 

We  have  now  reduced  the  circle  of  our  nearest  allies 
to  the  small  group,  containing  comparatively   few  foims, 


MANS   RELATION   TO  APES.  1 77 

which  is  represented  by  the  sub-order  of  the  Narrow-nosed, 
or  Eastern  Apes.  Finally,  the  question  which  now  re- 
mains to  be  answered  is — what  position  in  this  sub-order 
must  be  assigned  to  Man,  and  whether  other  inferences  as 
to  the  structure  of  our  immediate  ancestors  may  be  drawn 
from  this  position.  The  comprehensive  and  acute  researches 
into  the  Comparative  Anatomy  of  Man  and  the  various 
Catarhime,  which  Huxley  has  recorded  in  his  work  on  the 
"  Evidence  as  to  Man's  Place  in  Nature,"  are  of  the  greatest 
value  in  furnishing  the  answer  to  these  important  questions. 
The  inevitable  conclusion  is,  that  the  difference  between 
Man  and  the  highest  Narrow-nosed  Apes  (the  Gorilla,  Chim- 
panzee, Orang)  is  slighter  in  every  respect  than  the  corre- 
sponding differences  between  the  highest  and  the  lowest 
Catarhines  (the  Sea-cat,  Macaque,  Baboon).  Even  within 
the  small  group  of  the  Tail-less  man-like  Apes  (Anthro- 
poides)  the  several  genera  do  not  differ  less  from  each  other 
than  they  do  from  Men.  This  is  seen  by  a  glance  at  the 
skeletons  represented  here,  as  arranged  by  Huxley  (Figs. 
204-208).  If  the  skull,  or  the  vertebral  column,  together 
with  the  rib-system,  or  the  anterior  or  posterior  members, 
are  compared ;  or  if  the  comparison  is  extended  to  the 
muscular  system,  the  circulatory  system,  the  brain,  etc., 
a  candid  and  unprejudiced  examination  always  results  in 
the  same  conclusion,  that  Man  does  not  differ  more  from 
the  higher  Catarhines  than  the  extreme  forms  of  the  latter 
(for  example,  the  Gorilla  and  Baboon)  differ  from  each 
other.  We  can,  therefore,  complete  the  important  propo- 
sition already  quoted  from  Huxley  :  We  may  take  what- 
ever system  of  organs  we  will, — the  comparison  of  their 
modifications  within  the  ranks  of  the  Catarhinoo  leads  us 


i78 


THE   EVOLUTION   OF   MAN. 


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EVOLUTION  OF  MAN  FROM  APES.  1 79 

to  one  and  the  same  conclusion  :  that  the  anatomical  dif- 
ferences that  distinguish  Man  from  the  most  highly  developed 
Catarhinse  (the  Orang,  Gorilla,  Chimpanzee),  are  not  so  great 
as  those  which  separate  the  latter  from  the  lowest  Catarhinse 
(Sea-cat,  Macaque,  Baboon). 

We  must,  therefore,  consider  the  proof  complete,  that  Man 
is  descended  from  other  Narrow-nosed  Apes  (Catarhinai). 
Although  future  researches  into  the  Comparative  Anatomy 
and  Ontogeny  of  the  existing  Catarhines,  as  well  as  of  their 
fossil  relatives,  promise  us  various  new  details,  yet  no 
future  discovery  can  ever  overthrow  that  important  pro- 
position. Our  Catarhine  ancestors  must,  of  course,  have 
passed  through  a  long  series  of  varied  forms,  before  Man 
finally  developed  as  the  most  perfect  form.  The  following 
must  be  considered  as  the  most  important  advances  by 
which  this  "  Creation  of  Man,"  his  differentiation  from  the 
most  nearly  allied  Catarhine  Apes,  was  effected  :  Habituation 
to  upright  carriage  and,  in  connection  with  this,  the  greater 
differentiation  of  the  anterior  and  posterior  limbs ;  also,  the 
development  of  articulate  speech  and  its  organ,  the  larynx ; 
and  lastly,  and  especially,  the  more  perfect  development  of 
the  brain  and  its  function,  the  soul ;  sexual  selection  must 
have  exerted  an  extraordinarily  important  influence,  as 
Darwin  has  conclusively  proved  in  his  celebrated  work  on 
sexual  selection.162 

With  reference  to  these  advances,  we  may,  among  our 
Catarhine  ancestors,  distinguish  at  least  four  important 
ancestral  stages,  marking  prominent  epochs  in  the  great 
historical  process  of  the  origin  of  Man.  As  the  nineteenth 
stage  in  the  human  pedigree,  next  to  the  Semi-apes,  we  may 
place  the  oldest  and  lowest  Catarhine  Apes,  which  developed 


ISO  THE   EVOLUTION   OF  MAN. 

from  the  former  by  the  formation  of  the  characteristic 
catarhine  head,  and  by  the  peculiar  modification  of  the 
teeth,  the  nose,  and  the  brain.  This  oldest  parent-form  of 
the  whole  Catarhine  group  must,  certainly,  have  been 
thickly  covered  with  hair,  and  must  have  had  a  long  tail ; 
was,  in  fact,  a  Tailed  Ape  {Menocerca,  Fig.  203).  They 
were  already  in  existence  during  the  earlier  part  of  the 
Tertiary  Epoch  (during  the  Eocene  Period),  as  is  shown  by 
fossil  remains  of  Eocene  Catarhines.  Among  extant  Tailed 
Apes,  the  Slender  Apes  (Semnopitheci)  are  perhaps  most 
nearly  related  to  this  parent-form.163 

As  the  twentieth  stage  in  the  human  pedigree,  next  to 
these  Tailed  Apes,  we  must  rank  the  Tail-less  man-like  Apes 
(Anthropoides),  under  which  name  the  most  highly  de- 
veloped Catarhines,  those  most  nearly  related  to  Man,  have 
been  grouped.  They  originated  from  the  Tailed  Catarhines, 
by  the  loss  of  the  tail,  the  partial  loss  of  their  hairy  cover- 
ing, and  the  further  development  of  the  brain,  the  latter 
being  indicated  in  the  preponderating  development  of  the 
brain-skull  over  the  facial  skull.  At  the  present  time  but 
few  forms  of  this  remarkable  family  are  in  existence ;  they 
are  distributed  into  two  different  groups,  an  African  and  an 
Asiatic  group.  The  African  Man-like  Apes  are  limited  to 
the  western  part  of  tropical  Africa,  but  are  probably  dis- 
tributed over  Central  Africa  in  several  species.  Only  two 
species  are  well  known :  the  Gorilla  (Pongo  gorilla,  or 
Gorilla  eng'ina),  the  largest  of  all  Apes  (Fig.  207);  and  the 
smaller  Chimpanzee  {Pongo  troglodytes,  or  Engeco  troglo- 
dytes), which  may  be  seen  in  several  zoological  gardens 
(Figs.  206,  Plate  XIV.  Figs.  1,  2).  Both  the  African  Man- 
like Apes  are  black  in  colour,  and  like  their  countrymen, 


HAECKELS    EVOLUTION   OF    MAN. 


PL  A  TE  XIV. 


i.  Chimpanzei 


2.  Gorilla. 


4.  Negro. 


MAN-LIKE   APES.  l8l 

the  Negroes,  have  the  head  long  from  back  to  front  (doli- 
chocephalic). The  Asiatic  Man-like  Apes  are,  on  the  con- 
trary, mostly  of  a  brown,  or  yellowish  brown  colour,  and 
have  the  head  short  from  back  to  front  (brachycephalic), 
like  their  countrymen,  the  Malays  and  Mongols.  The 
largest  Asiatic  Man-like  Ape  is  the  well-known  Orang,  or 
Orang-outang  (Fig.  128),  which  is  indigenous  in  the  Sunda 
Islands  (Borneo,  Sumatra),  and  is  brown  in  colour.  Two 
species  have  recently  been  distinguished  :  the  great  Orang 
(Satyrus  Orang ;  Fig.  205,  Plate  XIV.  Fig.  3),  and  the  small 
Orang  (Satyrus  morio).  A  genus  of  smaller  Anthropoids 
(Fig.  204),  the  Gibbons  (Hylobates),  live  on  the  main-land 
of  Southern  Asia  and  on  the  Sunda  Islands ;  from  four  to 
eight  different  species  of  these  have  been  distinguished. 
Neither  of  these  living  Anthropoids  can  be  indicated  as  the 
Ape  absolutely  most  like  Man.  The  Gorilla  approaches 
nearest  to  Man  in  the  structure  of  the  hand  and  foot,  the 
Chimpanzee  in  important  structural  details  in  the  skull, 
the  Orang  in  the  development  of  the  brain,  and  the  Gibbon 
in  that  of  the  thorax.  It  is  evident  that  no  single  one  of 
these  existing  Man-like  Apes  is  among  the  direct  ancestors 
of  the  human  race  ;  they  are  all  the  last  scattered  remnants 
of  an  old,  catarhine  branch,  once  numerous,  from  which  the 
human  race  has  developed  as  a  special  branch  and  in  a 
special  direction. 

Although  Man  (Homo)  ranks  immediately  next  to  this 
anthropoid  family,  from  which  he  doubtless  directly  origin- 
ated, yet  the  Ape-men  (Pithecanthropi)  may  be  inserted 
here,  as  an  important  intermediate  form  between  the  two, 
and  as  the  twenty-first  stage  in  our  ancestral  series.  In  the 
"  Natural   History   of  Creation "  (vol.   ii.  p.  293),   I   have 


1 82  THE   EVOLUTION   OF   MAN. 

applied  this  name  to  the  speechless  Primitive  Men  (Alali), 
who  made  their  appearance  in  what  is  usually  called  the 
human  form,  that  is,  having  the  general  structure  of  Men 
(especially  in  the  differentiation  of  the  limbs) — but  yet 
being  destitute  of  one  of  the  most  important  qualities  of 
Man,  namely,  articulate  speech,  as  well  as  of  the  higher 
mental  development  connected  with  speech.  The  higher 
differentiation  of  the  larynx  and  of  the  brain  occasioned  by 
the  latter,  first  gave  rise  to  the  true  "  Man." 

Comparative  Philology  has  recently  shown  that  the 
present  human  language  is  polyphyletic  in  origin,  that 
several,  and  probably  many,  different  original  languages 
must  be  recognized,  as  having  developed  independently  from 
each  other.  The  history  of  the  development  of  languages 
also  teaches  us  (its  Ontogeny  in  every  child,  as  well  as  its 
Phylogeny  in  every  race),  that  the  actual  rational  lan- 
guage of  men  developed  gradually,  only  after  the  body 
had  developed  into  the  specific  human  form.  It  is  even 
probable  that  the  formation  of  language  did  not  begin  till 
after  the  differentiation  of  the  various  species,  or  races  of 
men,  and  this  presumably  occurred  in  the  beginning  of  the 
Quaternary  Epoch,  or  the  Diluvial  Period.  The  Ape-men, 
or  Alali,  were  therefore  probably  already  in  existence 
toward  the  close  of  the  Tertiary  Epoch,  during  the  Pliocene 
Period,  perhaps  even  as  early  as  the  Miocene  Period.161 

Lastly,  the  genuine  or  speaking  human  being  (Homo) 
must  be  considered  as  the  twenty-second  and  final  stage 
in  our  animal  pedigree.  Man  originated  from  the  pre- 
ceding stage  in  consequence  of  the  gradual  improvement 
of  inarticulate  animal  sounds  into  true  human  articulate 
peech.      Only  very  uncertain  conjectures  can  be  formed  as 


PlillMLEVAL   MAN.  1 83 

to  the  time  and  place  of  this  true  "  Creation  of  Man." 
It  is  probable  that  Primaeval  Man  originated  during  the 
Diluvial  Epoch,  in  the  torrid  zone  of  the  Old  World,  either 
on  the  continent  of  tropical  Asia  or  Africa,  or  on  an  earlier 
continent  which  has  now  sunk  belowthe  surface  of  the  Indian 
Ocean,  and  which  extended  from  Eastern  Africa  (Madajms- 
car  and  Abyssinia)  to  Eastern  Asia  (the  Sunda  Islands 
and  Eastern  India).  In  my  "  Natural  History  of  Creation  " 
(Chapter  XXIII.  and  Table  XV),  I  have  already  fully 
discussed  the  important  evidence  as  to  the  former  existence 
of  this  large  continent,  called  Lemuria,  and  how  the  distribu- 
tion of  the  various  species  and  races  of  men  probably  took 
place  from  this  "  Paradise  "  over  the  surface  of  the  earth. 
In  the  same  place,  I  have  also  fully  discussed  the  inter- 
relations of  the  various  races  and  species  of  the  human 
race.165 


TABLE    XXII. 

Systematic  Survey  or  the  Periods  in   the  Tiubal  History  of  Tne 

Human  Kace. 

(Compare  Table  VIII.,  vol.  i.  p.  402.) 


FIRST  MAIN  PERIOD  IN  TRIBAL   HISTORY. 

The  Plastid  Ancestors  of  Man. 
The  form  of  the  ancestors  of  man  is  equal  to  the  simple  individual  of  the 
first  order,  a  single  plastid. 

First  Stage  :  Moneron  Series  (Fig.  163,  p.  46). 
The  ancestors  of  man  are  single,  living,  simple  cytods. 

Second  Stage  :  Amoeba  Series  (Fig.  167  p.  53). 
The  ancestors  of  man  are  single,  living,  simple  cells. 

SECOND   MAIN   PERIOD   IN   TRIBAL   HISTORY. 
The  many-celled  Primitive  Animal  Ancestors  of  Man. 
The  ancestors  of  man  consist  of  a  closely -united  society  of  many  homo- 
geneous cells  ;  hence  their  form-value  is  that  of  individuals  of  the  second 
order,  of  Idorgana. 

Third  Stage  :  Synamoeba  Series  (Fig.  170,  p.  55). 

The  ancestors  of  man  are  many-celled  primitive  animals  of  the  simplest 
kind :  solid  masses  of  simple,  homogeneous  cells. 

Fourth  Stage  :  Planaea  Series  (Figs.  172, 173,  p.  60). 

The  ancestors  of  man  are  many-celled  primitive  animals  of  a  character 
like  that  of  the  Magosphwra  and  certain  planula-larvse,  of  equal  rank  with 
the  ontogenetic  Blastula  or  Blastosphcera ;  hollow  spheres,  the  wall  of  which 
consists  of  a  single  stratum  of  ciliated  cells. 


SYSTEMATIC   SURVEY   OF   THE  HUMAN    RACE.  185 

THIRD  MAIN  PERIOD  IN  TRIBAL  HISTORY. 

The  Invertebrate  Intestinal  Animal  Ancestors  of  Man. 

The  ancestors  of  man  have  the  form-value  of  individuals  of  the  third 
order,  of  inarticulate  individuals.  The  body  encloses  an  intestinal  cavity 
with  a  mouth,  and  consists  at  first  of  two  primary  germ-layers,  afterwards 
of  four  secondary  germ-layers. 

Fifth  Stage  :  Gastraea  Series  (Figs.  174-179,  p.  65). 

The  ancestors  of  man  have  the  form-value  and  structure  of  a  Gastrula. 
The  body  consists  merely  of  a  simple  primitive  intestine,  the  wall  of  which 
is  formed  of  the  two  primary  germ-layers. 

Sixth  Stage  :  Chordonium  Series  (Figs.  184-188,  p.  80-90). 

The  ancestors  of  man  are  worms  :  at  first,  primitive  worms,  allied  to  the 
Turbellaria;  afterwards  worms  of  higher  rank,  Scolecida;  finally,  notochord- 
animals  with  the  organization  of  the  ascidian  larvae.  The  body  is  composed 
of  foar  secondary  germ-layers. 


FOURTH  MAIN  PERIOD  IN  TRIBAL  HISTORY. 

The  Vertebrate  Ancestors  of  Man. 

The  ancestors  of  man  are  vertebrates,  and  their  form-value  is,  therefore, 
that  of  an  articulated  individual,  or  a  chain  of  metamera.  The  skin-sensory 
layer  is  specialized  into  the  horn-plate,  medullary  tube,  and  primitive 
kidneys.  The  skin-fibrous  layer  has  divided  into  the  leather-plate,  primitive 
vertebras  (muscular  plate  and  skeleton-plate),  and  the  notochord.  From 
the  intestinal-fibrous  layer  originates  the  heart  with  the  main  blood-vessels 
and  the  fleshy  intestinal  wall.  From  the  intestinal-glandular  layer,  the 
epithelium  of  the  intestinal  tube  is  formed.  The  formation  of  metamera  is 
constant. 

Seventh  Stage  :  Acrania  Series  (Fig.  189 ;  PI.  XL  Fig.  15). 

The  ancestors  of  man  arc  skull-less  vertebrates,  like  the  extant  Amphi- 
oxus.  The  body  already  forms  a  chain  of  metamera,  several  primitive 
vertebrae  having  separated  off.  The  head  is  not  yet  entirely  distinct  from 
the  trunk.  The  medullary  tube  has  not  separated  into  brain-bladders.  The 
heart  is  very  simple,  without  chambers.  The  skull  is  still  wanting;  as  are 
also  the  jaws  and  limbs. 


1 86  THE   EVOLUTION    OF   MAN. 

Eighth  Stage:  Monorhina  Series  (Fig.  190;  PI.  XI.  Fig.  16). 

The  ancestors  of  man  are  jaw-less  skulled  animals  (resembling  the 
developed  Myxinoides  and  Petromyzontes).  The  number  of  the  metamera  is 
increasing.  The  head  is  becoming  more  distinctly  differentiated  from  the 
trunk.  The  anterior  end  of  the  medullary  tube  swells  into  a  bladder-like 
structure  and  forms  the  brain,  which  is  soon  differentiated  into  five  brain- 
bladders.  At  the  sides  of  these  appear  the  three  higher  organs  of  sense. 
The  heart  is  divided  into  auricle  and  ventricle.  The  jaws,  limbs,  and 
swimming-bladder  are  still  wanting. 

Ninth  Stage  :  Ichthyoda  Series  (Figs.  191,  192;  PL  XII.  and  XIII.). 

The  ancestors  of  man  are  fish-like  skulled  animals :  first,  Primitive 
Fishes  (Selachii),  then  mud-fishes  (Pipneusta), then  gilled  Batrachians  (Sozura). 
The  ancestors  belonging  to  this  Ichthyoda  stage  develop  two  pairs  of  lirnbs : 
a  pair  of  anterior  limbs  (pectoral  fins)  and  a  pair  of  posterior  limbs  (ventral 
fins).  The  gill-arches  are  formed  between  the  gill-openings,  and  from  them 
are  formed  the  first  pair  of  jaw-arches  (upper  and  lower  jaws).  The 
swimming-bladder  (lungs),  liver,  and  pancreas  grow  from  the  intestinal 
canal. 

Tenth  Stage  :  Amniota  Series  (Figs.  195-208 ;   PI.  XIV.). 

The  ancestors  of  man  are  amnion -animals  or  gill-less  vertebrates  :  first, 
Primitive  amniota  (Protamnia),  then  Primitive  mammals  (Monotrema) ;  next, 
Pouched  animals  (Marsupialia)  :  then  Semi-apes  (Prosimicc),  and,  lastly, 
Apes  (Simiae).  The  ape-ancestors  of  man  are  first  tailed  Catarhini,  then 
tail-less  Catarhini  (Anthropoides),  then  speechless  Ape-men  (Alali),  and  at 
last  genuine,  speaking  men.  The  ancestors  belonging  to  this  amnionate 
series  develop  an  amnion  and  allantois,  and  gradually  acquire  the  mam- 
malian structure,  and  at  last  the  specific  human  form. 


(     i87    ) 


TABLE    XXIII. 

Systematic  Survey  of  the  Phylogenetic  Classification  of  Mammals. 


I. 

First 
Sub-cLss  of  " 

i      Cloacal 
Animals 

(Muixitrema,  or 

1.  Primitive  Mammals 

2.  Beaked  Animals 

fflammals 

,  Ornithodelphia) 

Promammalia 
Omithostoma 


II.  {     Pouched 

Second  I      Animals 

Sub-class  of  |  Qfarsupidlia,  or 

iHammals  *■      JHdelphia) 


3.  Herbivorous  Pouched  Animals 

4.  Carnivorous  Pouched  Animals 


Botanophaga 
Zoopkaga 


III. 

Third 
Sub-class  of 
fttammals : 

Placental 
Mammals 
[Plaeentalia, 

or  Mmio- 
dclpkia) 


III.  (a) 

Placental 
Mammals  with- 
out. Decidua,  with- 
Tufted  Placenta 

Indecidua 
Villiplacentalia 

III.  (6) 
Placental 

Mammals  with 

1  tecidua,  with 

Girdle  Placenta 

Deciduata 

Zonoplacentalia 


III.  (c) 

Placental 
Mammals  with 
Decidua,  with    \ 
Discoid  Placenta 

Deciduata 
Ditcqplacen  talia 


5.  Hoofed  Animals  f  Single-hoofed 
Ungulata         \  Double-hoofed 


6.  Whale-like 
Animals 
Vetumorplta 

1.  Pseudo-hoofed 

Animals 

Chelophora 

8.  Beasts  of  Prey 
Camassia 


Sea-cows 

Whales 


iRock  Conies 
Klephants 

Land  Beasts  of 

prey- 
Marine    Beasts 

prey 


9.  Ssmi-apes 
Prosimix 


/"Fingered  animals 
)  Dong-footed 
\  Flying  Lemur 
(  Lemurs 

0.  Gnawing     Ani-jE^S* 
J  Porcupine  species 
'  Hare  species 


mals 
Rodent  ia 


11.  Toothless 
Edentata 


12.  Insect-eaters 
Jnsectivora 


i  Digging  animals 
;  Sloths 

AVith  Ccecum 
Without  Ccecum 


13.  Flying  Animals  )  Flying  Foxes 
Cfiiroptera         \  Pats 


it.  Apes 
HimuB 


{  Flat-nosed 
Narrow-nosed  Apes 


Perizsodactyla 
Artiodactyla 

Sirenia 
Cetacea 


Lamnungia 
I'roboscidua 


Carnivora 
Pinnipedia 


J.eptolactyla 
Macrotarsi 
Ptenopleura 
Brachytarsi 

Sciuromorpha 
Myomorpha 
Hystrichomorpha 
Lagomorpha 

Bffodientia 
Bradypoda 

MenotypMa 
Lipotyphla 

Pterocynes 
Nycterides 

PlatyrhitHB 

Calarhince 


(     138     ) 

TABLE    XXIV. 

Pedigree  of  Mammals. 


Elephants 

Proboscidea 
Rock  Conies 

Lamnungia 


False-hoofed 

Chelophora  Flat-nosed  Apes 
Platyrhince 


fftan 
Homines 

Bats 
Man-like  Apes     Ny  derides 
Anthropoides 

|  Flying  Foxes 

Narrow-nosed  Apes     Pterocynes 
Catarhinm      JFIuing  Animals 
Chiroptera 


Sea  beasts  of  prey 
Pinnipedia 


©nanring  Animals         s v — - 

Kodentia  aprs 

Fingered  animals  Simise 

Whales         Leptodactyla 

Cetacea 

Sea-Cows 
Sirenia 
&23I)ak4amiln 
Cetomorpha 


Lemurs 
Brachytarsi 


Land  beasts  of  prey 
Carnivora 
Flying  Lemurs 
Ptenopleura     33 casts  of  IPrrg 

Carnassia 


Insect-eaters 
Long-footed  Insectivora 
Macrotarsi 


Toothless 

Edentata 


Joofctj  animals 
Ungulata 


SSHithout  Drritiua 
Indeciduata 


Semi-apes 
Prosimice 

Drciiuous  •animate 
Deciduata 


yiarrntal  Animals 
Placentalia 


Herbivorous  Pouched  Animals 
Marsupialia  botanophaga 


Carnivorous  Pouched  Animals 
Marsupialia  zoophaga. 


lpoud)rtJ  "animals 
Beaked  Animals  Marsupialia 

Ornithostoma 


Primitive  Mammals 
Promammalia 
©loacal  Animate 
Monotrema 


ha".ckel's  evolution  of  man. 


PEDIGREE  OF  MAN. 


PLATE  Xl\ 


(     i89    ) 

TABLE    XXV. 

Pedigree  of  Apes. 


fflan 
Homo 


Gorilla 

Chimpanzee     Gorilla 

Engeco 


■African 
fRan4ikc  ^pcs 


9pf4ikc  fflan 

Alalus 


Orang-Outang 

Satyrus  Gibbon 

Hylobates 


Asiatic 
i!Han4tke  8pcs 


£Han4tkc  Sines 

Aiithropoides 


Silk  Apes 
Hapalida 


Clutch-tails 
Labidocerca 


Flap-tails 

Aphyocerca 


Spcs  of  flrfo  Mtotttr 

Flat-nosed 
Platyrhinae 


Nose  Apes 
Tall  Apes  Nasalis 

Semnopithecus 


Sea  Cat 

Cercopithecus 


Catlrti  <3pcs 
Menocerca 


Spcs  of  ©IH  BiStorto 

Narrow-nosed 
Catarhinaa 


Baboons 

Cynocephalus 


<aprs 

SimiaB 


£cmwf3pr3 
Prosimiae 


CHAPTER  XX. 

THE   HISTORY   OF   THE   EVOLUTION   OF   THE   EPIDERMIS 
AND   THE   NERVOUS   SYSTEM. 

Aiiimal  and  Vegetative  Organ-systems. — Original  Relations  of  these  to  tlio 
Two  Primary  Germ-layers. — Sensory  Apparatus. — Constituents  of 
Sensory  Apparatus :  originally  only  the  Exoderm,  or  Skin-layer ;  after- 
wards, the  Skin-covering  specialized  from  the  Nerve-system. — Double 
Function  of  the  Skin  (as  a  Covering  and  as  Organ  of  Touch). — Outer 
Skin  (Epidermis)  and  Leather-skin  (Cort'um). — Appendages  of  the  Epi- 
dermis :  Skin-glands  (Sweat-glands,  Tear -glands,  Sebaceous  Glands, 
Milk-glands);  Nails  and  Hair. — The  Embryonic  Wool-covering. — Hair 
of  the  Head  and  of  the  Beard. — Influence  of  Sexual  Selection. — Arrange- 
ment of  the  Nerve-system. — Motor  and  Sensory  Nerves. — Central 
Marrow  :  Brain  and  Dorsal  Marrow. — Constitution  of  the  Human  Brain  : 
Large  Brain  {Cerebrum)  and  Small  Brain  (CerefceZJitm).— Comparative 
Anatomy  of  the  Central  Marrow. — Germ-history  of  the  Medullary-tube. 
— Separation  of  the  Medullary-tube  into  Brain  and  Dorsal  Marrow. 
— Modification  of  the  Simple  Brain-bladder  into  Five  Consecutive  Brain- 
bladders  :  Fore-brain  (Large  Brain,  or  Cerebrum),  T  wixt-brain  ("  Centre 
of  Sight "),  Mid-brain  ("  Four  Bulbs  "),  Hind-brain  (Small  Brain,  or  Cere- 
bellum),  After-brain  (Neck  Medulla). — Various  Formation  of  the  Five 
Brain-bladders  in  the  various  Vertebrate  Classes. — Development  of 
the  Conductive  Marrow,  or  "  Peripheric  Nervous  System." 

"  Hardly  any  part  of  the  bodily  frame,  then,  could  be  found  better 
calculated  to  illustrate  the  truth  that  the  structural  differences  between 
Man  and  the  highest  Ape  are  of  less  value  than  those  between  the  highest 


THE   DEVELOPMENT   OF   THE   ORGANS.  I9I 

and  the  lower  Apes,  than  the  hand  or  the  foot,  and  yet,  perhaps,  there  is  one 
organ  which  enforces  the  same  conclusion  in  a  still  more  striking  manner — 
and  that  is  the  brain." — Man's  Place  in  Nature,  p.  94  (1863). 

"  As  if  to  demonstrate,  by  a  striking  example,  the  impossibility  of 
erecting  any  cerebral  barrier  between  Man  and  the  Apes,  Nature  has 
provided  us,  in  the  latter  animals,  with  an  almost  complete  series  of  gra- 
dations, from  brains  little  higher  than  that  of  a  Rodent  to  brains  little  lower 
than  that  of  Man." — Ibid.  p.  96. 


Our  investigations,  up  to  the  present,  have  shown  us  how 
the  whole  human  body  has  developed  from  an  entirely  simple 
beginning,  from  a  single  simple  cell.  The  whole  human 
race,  as  well  as  the  individual  man,  owes  its  origin  to  a 
simple  cell.  The  one-celled  parent-form  of  the  former  is,  even 
yet,  reproduced  in  the  one-celled  germ-form  of  the  latter. 
In  conclusion,  we  must  glance  at  the  evolutionary  history  of 
the  separate  parts  which  constitute  the  human  body.  In 
this  matter,  I  must,  of  course,  restrict  myself  to  the  most 
general  and  important  outlines  ;  for  a  detailed  study  of  the 
evolutionary  history  of  the  separate  organs  and  tissues 
would  occupy  too  much  space,  and  would  demand  a  greater 
extent  of  anatomical  knowledge  than  the  generality  of  my 
readers  are  likely  to  possess.  In  considering  the  develop- 
ment of  the  organs,  and  of  their  functions,  we  will  retain  the 
method  previously  employed,  except  that  we  will  consider 
the  germ-history  and  the  tribal  history  of  the  various  parts 
of  the  body  in  common.  In  the  history  of  the  evolution  of 
the  human  body  as  a  whole  we  have  found  that  Phylogeny 
everywhere  serves  to  throw  light  on  the  obscure  course  of 
Ontogeny,  and  that  the  clew  afforded  by  phylogenetic  con- 
tinuity alone  enables  us  to  find  our  way  through  the  labyrinth 
of  ontogenetic  facts.  We  shall  experience  exactly  the  same 
fact  in   the  history   of   the   development  of  the  separate 


192  THE   EVOLUTION   OF   MAN. 

organs  ;  but  I  shall  be  compelled  to  explain  the  ontogenetic 
and  the  phylogenetic  origin  of  the  organs  simultaneously ; 
for  the  further  we  penetrate  into  the  details  of  organic 
development,  and  the  more  minutely  we  study  the  origin 
of  the  separate  parts,  the  more  clearly  do  we  see  how 
inseparably  the  evolution  of  the  germ  is  connected  with 
that  of  the  tribe.  The  Ontogeny  of  the  organs  is  intelligible 
and  explicable  only  through  their  Phylogeny ;  just  as  the 
germ -history  of  the  entire  body  (the  "person")  is  rendered 
intelligible  only  by  the  history  of  the  tribe.  Each  germ- 
form  is  determined  by  a  corresponding  ancestral  form.  This 
is  as  true  of  the  parts  as  of  the  whole. 

In  endeavouring,  with  the  help  of  this  fundamental  law 
of  Biogeny,  to  obtain  a  general  view  of  the  main  features  in 
the  development  of  the  separate  organs  of  man,  we  must,  in 
the  first  place,  consider  the  animal,  and  then  the  vegetative 
organ-systems  of  the  body.  The  first  main  group  of  organs, 
the  animal  organ-systems,  is  formed  by  the  sensory  apparatus, 
together  with  the  motor  apparatus.  To  the  former  belong 
the  skin-covering,  the  nervous  system,  and  the  organs  of  the 
senses.  The  motor  apparatus  consists  of  the  passive  organs 
of  movement  (the  skeleton)  and  the  active  organs  (the 
muscles).  The  second  main  group  of  organs,  the  vegetative 
organ-system,  is  formed  by  the  nutritive  and  the  repro- 
ductive apparatus.  To  the  nutritive  apparatus  belongs 
especially  the  intestinal  canal  with  all  its  appendages, 
together  with  the  vascular  and  renal  systems.  The  repro- 
ductive apparatus  includes  the  various  sexual  organs  (the 
germ-glands,  germ-ducts,  organs  of  copulation,  etc.). 

In  earlier  chapters  (IX.  and  X.)  it  has  been  stated  that 
the  animal  organ-systems  (the  instruments  of  sensation  and 


ANIMAL   AND    VEGETATIVE   ORGAN-SYSTEMS.  1 93 

of  movement)  proceed  especially  from  the  outer  primary 
germ-layer,  from  the  skin-layer.  The  vegetative  organ- 
systems,  on  the  other  hand  (the  instruments  of  nutrition  and 
reproduction),  proceed  principally  from  the  inner  primary 
germ-layer,  from  the  intestinal  layer.  This  radical  contrast 
between  the  animal  and  the  vegetative  spheres  of  the  body 
is,  it  is  true,  by  no  means  absolute  either  in  man  or  in  the 
higher  animals ;  on  the  contrary,  many  separate  parts  of  the 
animal  apparatus  {e.g.,  the  intestinal  nerve,  or  sympathetic) 
originated  from  cells  which  have  proceeded  from  the  ento- 
derm ;  and,  on  the  other  hand,  a  large  part  of  the  vegetative 
apparatus  {e.g.,  the  mouth-cavity,  and  probably  the  greater 
part  of  the  urinary  and  sexual  organs)  is  formed  of  cells 
which  are  originally  derived  from  the  exoderm.  Moreover, 
in  the  bodies  of  all  the  more  highly  developed  animals,  the 
most  heterogeneous  parts  are  so  intermixed  and  blended 
that  it  is  often  extremely  difficult  to  assign  its  true  source 
to  each  one  of  the  constituent  parts.  But,  on  the  whole,  we 
may  assume  as  a  certain  and  important  fact,  that  in  Man, 
and  in  all  high  animals,  the  greater  part  of  the  animal  organs 
must  be  referred  to  the  skin-layer,  or  exoderm ;  the  greater 
part  of  the  vegetative  organs  to  the  intestinal  layer,  or 
entoderm.  For  this  reason,  Baer  called  the  former  the 
animal  germ-layer,  the  latter,  the  vegetative  germ-layer 
(Cf.  vol.  i.  pp.  53  and  19G).  Of  course,  in  making  this  important 
assumption,  we  pre-suppose  the  correctness  of  Baer's  view, 
according  to  which  the  skin-fibrous  layer  (the  "flesh 
stratum"  of  Baer)  must  have  originated  (phylogenetically) 
from  the  exoderm,  and,  on  the  other  hand,  the  intestinal- 
fibrous  layer  (Baer's  "vascular  layer")  from  the  entoderm. 
This  influential  view,  which  is  yet  much  disputed,  is,  we 


(     194    ) 


TABLE    XXVI, 

Systematic  Survey  of  the  Organ- Systems  of  the  Human  Body. 
(N.B. — The  origin  of  the  separate  organs  from  the  four  secondary  germ- 
layers  is  indicated  by  the  Roman  numerals  (I. -IV.)  :  I.  Skin-sensory  layer; 
II.   Skin-fibrous  layer ;   III.  Intestinal-fibrous  layer ;   IV.  Intestinal-gland, 
ular  layer.) 


H 
co 

r. 

cd 
o 

j 
g 

s 


A. 

Sensory 

Apparatus 

Scnsorium 


f\.  Skin-covering       f  Outer  skin 
(Derma)  \  Leather  tkin 


2.  Central    nerve- 
system 


(  Brain 

\  Spinal  marrow 


B. 

Motive 
Apparatus 
Locomotorium 


„   n    ■  i     •     „_  ~    I  Brain  nerves 
3.Penphencnerve-lSpinalnerveg 

system  |  Intestinal  nerves 

(Organ  of  touch  (skin) 
Organ  of  taste  (tongue') 
Or.an  of  smell  (nose) 
Organ  of  sight  (eye) 
Organ  of  hearing  (ear)      Org.  auditus 


Epidermis,  I. 

Corium,  II. 

Encephalon  )  » 

Medulla  spinalis  ) 

Kervi  cerebrates,  I.  +  II 
A'ervi  spinales,  II. 
Sympatheticus.il. + III. 

Org  tactus 
Org.  gustus 
Org.  olfactus 


Org.  visus 


\  I.  +  II. 


(B.    Muscle  -  system  j  sw  j  UvsenK  cutane 

(active  motive  I  slieleton  musclea  M  skeleti 
organs)              \ 

6.    Skeleton-system  I  Vertebral  column  Vertebrarium 

(passive motive  <  Skull  Cranium 

organs)  [  Limb  skeleton  Sk.  extremitatum 


II. 


°1 


C. 

Nutritive 
Apparatus 
NutritoTium 


(1.  Intestinal  system 
(Gaster) 

8.  Vascular  system 
(Organa  circa- 
lalionis) 


0.  Renal  system 
(Oryana  urinaria) 


D. 

Reproductive 
Apparatus  s 
Propagator  ium 


10    Sexual  organs 
(Oryana  sexual  ia) 


Digestive  organ 
Respiratory  organ 

Body  cavity 
Lymph  vessels 

Blood  vessels 
Heart 

(  Kidneys 

<  Urinary  ducts 

[  Urinary  bladder 

(Sexual  glands 
(I.  Ovarv) 
(II.  Testes) 
Sexual  ducts 
(I.  Oviduct) 

(II.  Seed  duct) 

Copulatory  organs 
(I.  Sheath) 
(II.  Tenia) 


0.  digestiva    ■) 
O.respiratoriaJ 


III.  +  1V. 


Coeloma,  II.  +  III. 
Vasa  lympha- ) 

tica  ill.  +  III. 

V.  sanguifera  | 

Cor,  III. 

Ureteres  )  L  CO  +  n- 
Urocystis,  III.  +  IV. 

Gonades 

(I.  Ovaria)III.  +  IV.(?) 

(II.  Testes)  I.  +  II.  (r) 

Gonophori     . 

(1.  Oviduc- 

tus)  }I.(?)  +  II. 

(II.  Sperma-1 

ductus)      / 
Copulativa  \ 
aa)  >  I 


(I.  Vagina)  ,. 
(II.  Penis)  | 


+  JI. 


THE  SENSORY  APPARATUS.  1 95 

think,  securely  founded  on  the  Gastrula — that  most  impor- 
tant of  all  the  germ-forms  of  the  animal  kingdom — which 
Ave  find  recurs  in  similar  form  in  the  germ-history  of  the 
most  different  classes  of  animals.  This  significant  germ- 
form  points  unmistakably  to  a  parent-form  (the  Gastraea) 
common  to  all  animals,  the  Protozoa  alone  excepted  ;  in 
this  long  extinct  parent-form  the  entire  body  of  the  animal 
consisted  throughout  life  of  the  two  primary  germ-layers,  as 
is  yet  the  case,  for  a  short  time,  in  the  Gastrula.  In  the 
Gastraea  the  simple  skin-layer  did  actually  represent  all  the 
animal  organs  and  functions,  and  the  simple  intestinal  layer, 
on  the  other  hand,  all  the  vegetative  organs  and  functions ; 
potentially,  this  is  even  yet  the  case  in  the  Gastrula. 

In  studying  the  development  of  the  first  important 
part  of  the  animal  sphere,  the  sensory  apparatus,  or  sen- 
sorium,  we  shall  now  find  how  well  adapted  this  Gastraea 
Theory  is  to  explain,  not  only  in  a  morphological  but 
in  a  physiological  sense,  the  most  important  facts  in  the 
history  of  evolution.  This  sensory  apparatus  consists  of  two 
very  distinct  parts,  having,  apparently,  nothing  in  common  : 
in  the  first  place,  the  external  skin-covering  {Derma), 
together  with  its  appendages,  the  hair,  nails,  sweat-glands, 
etc. ;  and,  secondly,  the  nervous  system,  situated  internally. 
The  latter  includes  the  central  nervous  system  (brain  and 
spinal  chord),  the  peripheric  brain-nerves  and  medullary 
nerves,  and  finally,  the  organs  of  sense.  In  the  fully 
developed  vertebrate  body  these  two  main  constituents  of 
the  sensorium  are  entirely  separate ;  the  skin  lying  entirely 
externally  on  the  body,  while  the  central  nervous  system 
is  within,  and  quite  separate  from  the  former.  The  two 
are  connected  merely  by  a  portion  of  the  peripheric  nerve- 


I96  THE   EVOLUTION   OF   MAN. 

system  and  of  the  sense-organs.  And  yet,  as  we  already 
know  from  the  germ-history  of  man,  the  latter  is  developed 
from  the  former.  Those  organs  of  our  body  which  discharge 
the  highest  and  most  perfect  functions  of  animal  life — those 
of  sensation,  volition,  thought — in  a  word,  the  organs  of 
the  psyche,  of  mental  life — arise  from  the  external  skin- 
covering. 

This  remarkable  fact,  considered  in  itself  alone,  seems  so 
wonderful,  inexplicable,  and  paradoxical,  that  the  truth  of  the 
fact  was  simply  long  denied.  The  most  trustworthy  embryo- 
logical  observations  were  met  with  the  erroneous  statement 
that  the  central  nerve-system  develops,  not  from  the  outer 
germ-layer,  but  from  a  special  cell-layer  lying  underneath 
this.  The  ontogenetic  fact  would  not,  however,  yield ;  and, 
now  that  Phylogeny  has  thrown  light  on  the  subject,  the 
fact  seems  perfectly  natural  and  necessary.  When  we 
reflect  on  the  historic  evolution  of  mind  and  sense  activities, 
we  must  necessarily  conceive  the  cells,  which  accomplish 
these,  as  originally  situated  on  the  outer  surface  of  the 
animal -body.  Such  externally  placed  elementary  organs 
could  alone  directly  receive  and  deal  with  impressions  from 
the  outer  world.  Afterwards,  under  the  influence  of 
natural  selection,  the  complex  cell-masses  which  had  become 
especially  "  sensitive  "  gradually  withdrew  into  the  shelter  of 
the  interior  of  the  body,  and  there  laid  the  first  foundations 
of  a  central  nervous  organ.  As  differentiation  advanced, 
the  distance  and  distinstion  between  the  external  skin- 
covering  and  the  central  nervous  system  detached  from  this, 
became  continually  greater,  and  finally  the  two  were  per- 
manently connected  merely  by  the  conductive  peripheric 
nerves. 


DERMIC   ORIGIN   OF   THE   SENSORY   ORGANS.  1 97 

This  view  is  fully  confirmed  by  the  results  of  Comparative 
Anatomy.  Comparative  Anatomy  shows  that  many  lower 
animals  possess  no  nervous  system,  although,  in  common 
with  higher  animals,  they  exercise  the  functions  of  sensation, 
volition, and  thought.  In  the  Primitive  Animals  (Protozoa), 
which  do  not  even  form  germ-layers,  of  course  the  nervous 
system,  like  the  skin-covering,  is  wanting.  Even  in  the 
second  main  division  of  the  animal  kingdom — in  the  Metazoa 
or  Intestinal  Animals — there  is  at  first  no  nervous  system. 
The  functions  of  these  are  performed  by  the  simple  cell- 
layer  of  the  exoderm,  which  the  lower  Intestinal  Animals 
have  inherited  directly  from  the  Gastrpea  (Fig.  209,  e).  This 
is  the  case  in  the  lowest  Plant  Animals  (Zoophyta),  the  Gas- 
treads,  Sponges,  and  the  lowest  Hydroid  Polyps,  which  are 
but  little  higher  than  the  Gastraeads.  Just  as  all  the  vege- 
tative functions  of  these  are  performed  by  the  simple  intes- 
tinal layer,  so  all  the  animal  functions  are  discharged  by 
the  equally  simple  skin-layer.  The  simple  cell  stratum  of 
the  exoderm  is,  in  these,  skin-covering,  motive  apparatus, 
and  nervous  system  simultaneously. 

Most  probably  the  nervous  system  was  also  wanting  in  a 
large  proportion  of  those  Primitive  Worms  (Archelminthes) 
which  were  developed  directly  from  the  Gastrseads.  Even 
those  Primitive  Worms  in  which  the  two  primary  germ-layers 
had  already  split  into  the  four  secondary  germ-layers  (Plate 
V.  Fig.  10),  seem  not  to  have  possessed  a  nervous  system 
distinct  from  the  skin.  The  skin-sensory  layer  must,  even  in 
these  long-extinct  Worms,  have  been  at  once  skin-covering 
and  nerve-system.  But  already  in  the  Flat  Worms  (Platel- 
minthcs),  and  especially  in  the  Gliding  Worms  {Tuvbellaria) 
which  of  all  existing  forms  approach  nearest  to  the  Primitive 


198 


THE   EVOLUTION   OF   MAN. 


Worms,  we  find  an  independent  nerve-system,  distinct  and 
separate  from  the  outer  skin-covering.     This  is  the  "  upper 


Fig.  209. — Gastrnla  of  Gastrophysema  (Gastraad-class). 

Fig.  210. — Transverse  section  through  an  embryonic  Earth-worm  :  hs, 
skin-sensory  layer;  hm,  skin-fibrons  layer;  (7/,  intestinal-fibrous  layer;  dd, 
intestinal-glandular  layer  ;  a,  intestinal  cavity  ;  c,  body-cavity,  or  Cceloma  ; 
n,  nerve-ganglia;  u,  primitive  kidneys. 

Fig.  211. — A  Gliding  Worm  (Rhabdoccelum) .  From  the  brain  or  upper 
throat  ganglion  (g)  nerves  (n)  radiate  towards  the  skin  (/),  the  eyes  (an), 
the  organ  of  smell  (na),  and  the  mouth  (m)  :  h,  testes;  e,  ovaries. 


THE   SKIN.  199 

throat  ganglion/'  situated  above  the  throat  (Fig.  211,  g ;  Plate 
V.  Fig.  11,  til).  The  complex  central  nervous  system  of  all 
higher  animals  has  developed  from  this  simple  rudiment. 
In  the  higher  Worms,  e.g.,  the  Earth-worms,  according  to 
Kowalevsky,  the  earliest  rudiment  of  the  central  nervous 
system  (Fig  210,  n)  is  a  local  thickening  of  the  skin- 
sensory  layer  (Its),  which  afterwards  becomes  entirely 
detached  from  the  horn-plate.  Even  the  medullary  tube  of 
Vertebrates  has  the  same  origin.  From  the  germ-history 
of  Man,  we  already  know  that  this  medullary  tube,  the 
commencement  of  the  central  nervous  system,  originally 
develops  from  the  outer  skin-covering. 

Let  us  now  turn  aside  from  these  very  interesting- 
features  in  evolution,  and  examine  the  development  of  the 
later  human  skin-covering,  with  its  hairs,  sweat-glands,  etc. 
Physiologically,  this  outer  covering  (derma,  or  tegumentum) 
plays  a  double  part.  The  skin,  in  the  first  place,  forms  the 
general  protective  covering  (integwmcntiim  commune)  which 
covers  the  whole  surface  of  the  body,  and  protects  all  other 
parts.  As  such,  it,  at  the  same  time,  effects  a  certain  ex- 
change of  matter  between  the  body  and  the  surrounding 
atmospheric  air  (perspiration  or  skin-breathing).  In  the 
second  place,  the  skin  is  the  oldest  and  most  primitive 
sense-organ,  the  organ  of  touch,  which  effects  the  sensation 
of  the  surrounding  temperature  and  of  the  pressure  or  re- 
sistance of  bodies  with  which  it  comes  in  contact. 

The  human  skin,  like  that  of  all  higher  animals,  consists 
essentially  of  two  distinct  parts ;  of  the  outer-skin,  and  of 
the  underlying  leather-skin.  The  outer-skin  (epidermis) 
consists  only  of  simple  cells,  and  contains  no  blood-vessels 
(Fig.  212,  ab).  It  develops  from  the  first  of  the  secondary 
32 


200 


THE   EVOLUTION   OF  MAN. 


germ-layers  from  the  skin-sensory  layer,  and,  directly,  from 
the  horn-plate  of  the  latter.  The  leather-skin  (corium),  on 
the   contrary,  consists  principally   of  connective  or  fibrous 


Fig.  212. — Human  skin 
in  perpendicular  section 
(after  Ecker),  much  en- 
larged :  o,  horny  stratum  of 
outer-skin  (epidermis)  ;  b, 
mucous  stratum  of  outer- 
skin  ;  c,  papillae  of  the 
leather-skin  (corium) ;  d, 
blood-vessels  of  the  latter  ; 
e,  f,  excretory  ducts  of  the 
sweat-glands  (<y) ;  h,  fat- 
globules  of  the  leather-skin ; 
i,  nerve,  passing  above  into 
a  touch-body. 


tissue,  contains  numerous  blood-vessels  and  nerves,  and  has 
a  different  origin.  It  develops  from  the  outer  stratum  of 
the  second  secondary  germ-layer,  from  the  skin-fibrous  layer. 
The  leather-skin  is  much  thicker  than  the  outer-skin.  In 
its  deeper  part,  the  "  subcutis,"  lie  many  masses  of  fat-cells 
(Fig.  212,  h).  Its  upper  part,  the  true  "cutis,"  or  papillary 
layer,  forms,  over  nearly  the  whole  surface  of  the  body,  a 
number  of  microscopic  cone-shaped  warts,  or  papillae,  which 
fit  into  the  overlying  epidermis  (c).  These  touch-warts,  or 
sensory  papillae,  contain  the  most  delicate  of  all  the  sensory 
organs  of  the  skin,  the  '■  corpuscula  tactas"     Other  papillae 


STRUCTURE   OP   THE   SKIN.  201 

contain  merely  the  terminal  loops  of  the  nutritive  blood- 
vessels of  the  skin  (cd).  All  these  different  parts  of  the 
leather-skin  originate,  by  differentiation,  from  the  cells,  origi- 
nally homogeneous,  of  the  leather-plate,  the  outer  lamella 
of  the  skin-fibrous  layer  (Fig.  112,hpr,  vol.  i.  p.  352;  Plates  IV. 
and  V.,  I ;  Figs.  65-69,  hf,  p.  277).106 

Analogously,  all  the  constituent  parts  and  appendages  of 
the  outer-skin  {epidermis)  originate,  by  differentiation,  from 
the  homogeneous  cells  of  the  horn-plate  (Fig.  213).     At  a 


Fig.  213. — Cells  of  the  outer-skin  (epidermis)  of 
a  human  embryo  of  two  months.     (After  Koelliker.) 


very  early  period,  the  simple  cell-layer 
of  this  horn-plate  splits  into  two  dis- 
tinct strata.  The  inner,  softer  stratum 
(Fig.  212,  b)  is  called  the  mucous  layer; 
the  outer,  harder  stratum  (a),  the  horn-layer  of  the  outer- 
skin.  The  surface  of  this  horn-layer  is  continually  worn 
out  and  thrown  off;  new  cell-strata,  produced  by  the 
growth  of  the  underlying  mucous  layer,  take  its  place. 
Originally  the  outer-skin  forms  an  entirely  simple  cover 
over  the  surface  of  the  body.  Afterwards,  however,  sundry 
appendages  develop  from  this  both  internally  and  ex- 
ternally. The  internal  appendages  are  the  skin-glands ; 
the  sweat-glands,  the  sebaceous  glands,  etc.  The  external 
appendages  are  hair,  nails,  etc. 

The  glands  of  the  skin-covering  are  at  first  merely 
solid  plug-shaped  growths  of  the  outer-skin  (epidermis), 
which  penetrate  into  the  underlying  leather-skin  (corium) 
(Fig.  214!).      A  canal  afterwards  forms  inside  these  solid 


202 


THE   EVOLUTION    OF   MAN. 


plugs  (2,  3),  either  owing  to  the  softening  and  breaking 
up  of  the  central  cells,  or  as  the  result  of  a  fluid  internally 
secreted.  Some  of  these  skin-glands  remain  unbranched,  as, 
for  instance,  the  sweat-glands  (e,f,g).  These  glands,  which 
secrete  the  sweat,  are  of  great  length,  their  ends  forming  a 
coil ;  they  never  branch,  however ;  and  the  same  is  to  be 
said  of  the  glands  which  secrete  the  fatty  wax  of  the  ears. 


Fig.  214. — Rudiments  of  tcar-glands 
from  a  human  embryo  of  four  months. 
(After  Koelliker.)  1.  Earliest  rudiment  the 
shape  of  a  simple,  solid  plug.  2  and  3.  Fur- 
ther developed  rudiments,  which  branch 
and  become  hollow  :  a,  a.  solid  offshoot ; 
e,  cell-covering  of  the  hollow  offshoot ;  /, 
rudiment  of  the  fibrons  covering,  which 
afterwards  forms  the  leather-skin  round 
the  glands. 

Most  other  skin-glands  give  out 
shoots  and  branches,  as,  for  in- 
stance, the  tear-glands,  situated 
on  the  upper  eyelid,  which  secrete 
the  tears  (Fig.  214),  and  also  the 
sebaceous  glands,  which  produce  the  fatty  sebaceous  matter, 
and  generally  open  into  the  hair-follicles.  The  sweat 
and  sebaceous  glands  occur  only  in  Mammals.  The  tear- 
glands,  on  the  contrary,  are  found  in  all  the  three  classes  of 
Amnion  Animals,  in  Reptiles,  Birds,  and  Mammals.  They 
are  not  represented  in  the  lower  Vertebrates. 

Very  remarkable  skin-glands,  found  in  all  Mammals, 
and  in  them  exclusively,  are  the  milk-glands  (glandulce 
mammales,  Figs.  215,  216).  They  supply  milk  for  the 
nourishment  of  the  new-born  Mammal.     Notwithstanding 


SKIN-GLANDS. 


lO$ 


their  extraordinary  size,  these  important  organs  are  merely 
large  sebaceous  skin-glands  (Plate  V.  Fig.  16,  md).  The 
milk  is  produced  by  liquefaction  of  the  fatty  milk-cells 
within  the  branched  milk-gland  pouch  (Fig.  215,  c),  just 
as  the  sebaceous  matter  of  the  skin,  and  the  fatty  matter 
of  the  hair  are  produced  by  the  breaking  up  of  fatty 
sebaceous  cells  within  the  sebaceous  skin-glands.  The 
excretory  passages  of  the  milk-glands  enlarge  into  sac-like 
milk-ducts  (6),  which  again  become  narrower  (a),  and  open, 
through  from  sixteen  to  twenty-four  minute  apertures,  into 
the  nipple  of  the  breast.  The  first  rudiment  of  this  large 
and  complex   gland  is  a  very  simple  conical  plug  in  the 


Fig.  215. — The  breast  of  the  female  in  section  :  c,  grape-like  glandular 
lobnles  ;  b,  enlarged  milk-ducts;  a,  narrow  excretory  ducts,  opening  through 
the  breast-nipple.     (After  H.  Meyer.) 

Fig.  216. — Milk-glands  of  a  new-born  child  :  a,  original  central  gland; 
b,  smaller,  and  c,  larger  branches  of  the  latter.     (After  Langer.) 


204  THE   EVOLUTION   OF   MAN. 

outer-skin  (epidermis),  which  extends  into  the  leather-skin 
(corivAn),  and  there  branches.  In  the  new-born  child  it 
consists  merely  of  from  twelve  to  eighteen  radiating  lobules 
(Fig.  216).  These  gradually  branch,  the  excretory  passages 
become  hollow,  and  a  large  quantity  of  fatty  matter  collects 
between  the  lobules.  Thus  is  developed  the  prominent 
breast  of  the  female  (mamma),  on  the  summit  of  which 
rises  the  nipple'  (mammilla),  adapted  for  being  sucked.167 
The  nipple  does  not  appear  until  after  the  milk -gland 
is  already  formed;  this  ontogenetic  phenomenon  is  very 
interesting,  because  the  more  ancient  Mammals  (the  parent- 
forms  of  the  entire  class)  had  no  nipples.  In  them,  the  milk 
simply  emerged  through  a  plane,  sieve-like  perforated  spot 
in  the  abdominal  skin,  as  is  even  now  the  case  in  the  lowest 
extant  Mammals,  the  Beaked  Animals  (Monotremata ;  p.  14G). 
On  account  of  this  character  these  animals  may  be  called 
Amasta  (without  nipple).  In  many  of  the  lower  mammals 
there  are  numerous  milk-glands,  situated  at  various  points  of 
the  ventral  side.  In  the  human  female  there  is  usually  only 
a  pair  of  milk-glands,  placed  on  the  point  of  the  breast,  as  in 
Apes,  Bats,  Elephants,  and  some  other  Mammals.  Occasion- 
ally, however,  even  in  the  human  female  two  pairs  of  breast 
glands  (or  even  more)  appear,  lying  one  behind  the  other ; 
this  must  be  regarded  as  a  reversion  to  an  older  parent- 
form.  Sometimes  these  glands  are  well  developed  even  in 
the  male,  and  are  capable  of  being  sucked,  though  as  a  rule 
they  exist  in  the  male  sex  only  as  rudimentary  organs  with- 
out function. 

Just  as  the  skin  glands  originate  as  local  growths  of 
the  outer  skin  in  an  inward  direction,  so  the  appendages 
of  the  skin,  called  hair  and  nails,  originate  as  local  growths 


EXTERNAL  APPENDAGES  OF  THE  SKIN.       205 

of  the  outer  skin  in  an  outward  direction.  The  nails  (un- 
gues), which  are  important  protective  formations  over  the 
hind  surface  of  the  most  sensitive  parts  of  our  limbs — the 
tips  of  the  fingers  and  toes — are  horny  products  of  the 
epidermis,  common  to  us  with  the  Apes.  In  their  place, 
the  lower  Mammals  generally  possess  claws,  and  the 
Hoofed  Animals  (Ungulata)  hoofs.  The  parent-form  of 
Mammals  undoubtedly  had  claws,  such  as  appear  in  a 
rudimentary  state  in  the  Salamander.  The  hoofs  of  the 
Hoofed  Animals  and  the  nails  of  Apes  and  of  Man  originated 
from  the  claws  of  more  ancient  Mammals.  In  the  human 
embryo  the  first  rudiment  of  the  nails  first  appears  (between 
the  horn-layer  and  the  mucous  layer  of  this  outer  skin) 
in  the  fourth  month.  Their  edges  do  not,  however,  project 
until  the  end  of  the  sixth  month. 

The  most  interesting  and  important  appendages  of  the 
outer  skin  are  the  hairs,  which,  on  account  of  their  peculiar 
structure  and  mode  of  origin,  must  be  regarded  as  very 
characteristic  of  the  whole  Mammalian  class.  Hairs,  it  is 
true,  appear  widely  distributed  in  many  lower  animals,  e.g., 
in  Insects  and  Worms.  But  these  hairs,  like  those  of  plants, 
are  thread-like  processes  of  the  outer  surface,  and  differ 
from  Mammalian  hairs  in  their  characteristically  finer 
structure  and  in  their  mode  of  development.  Hence  Oken 
rightly  called  Mammals  "hairy  animals."  The  hairs  of 
Man,  as  of  all  other  Mammals,  consist  simply  of  epidermic 
cells  peculiarly  differentiated  and  arranged.  In  their  first 
state,  they  appear  in  the  embryo  as  solid  plug-shaped  pro- 
cesses of  the  epidermis  which  penetrate  into  the  underlying 
leather-skin  (corium),  as  do  the  sebaceous  and  the  sweat 
glands.     As  in  the  latter,  the  simple  plug  consists  originally 


206  THE  EVOLUTION   OF  MAN. 

of  the  ordinary  epidermic  cells.  Within  this  a  firmer 
central  cellular  mass  of  conical  shape  soon  forms.  This 
increases  considerably  in  length,  detaches  itself  from  the 
surrounding  cellular  mass,  the  "root-sheath,"  and  finally 
makes  its  way  to  the  outside,  appearing  above  the  outer 
surface  as  a  hair-stem.  The  deepest  part,  buried  in  the 
skin,  the  hair  follicle,  is  the  root  of  the  hair,  and  is  sur- 
rounded by  the  root-sheath.  In  the  human  embryo  the 
first  hairs  make  their  appearance  at  the  end  of  the  fifth 
or  in  the  becdnnincj  of  the  sixth  month. 

During  the  last  three  or  four  months  before  birth  the 
human  embryo  is  usually  covered  by  a  thick  coating  of  deli- 
cate woolly  hairs.  This  embryonic  wool-covering  (lanugo) 
is  often  lost  during  the  last  weeks  of  embryonic  life,  and, 
at  any  rate,  soon  after  birth,  when  it  is  replaced  by  the 
thinner  permanent  hair-covering.  These  later  permanent 
hairs  grow  out  of  hair  follicles  which  are  developed  from 
the  root-sheaths  of  the  deciduous  woolly  hair.  In  the 
human  embryo,  the  embryonic  woolly  hair  usually  covers 
the  entire  body,  with  the  exception  of  the  palms  of  the 
hands  and  the  soles  of  the  feet.  These  parts  remain  bare, 
just  as  in  all  Apes  and  most  other  Mammals.  Not  un- 
frequently  the  woolly  coat  of  the  embryo  differs  considerably 
in  colour  from  the  later  permanent  hairy  covering.  Thus 
for  instance,  it  sometimes  happens  in  our  own  Indo-Ger- 
manic  race  that  fair-haired  parents  are  shocked  to  find 
their  children,  at  their  first  appearance,  covered  by  a  dark 
brown,  or  even  black,  woolly  covering.  It  is  only  after  this 
has  been  shed,  that  the  permanent  fair  hair,  which  the 
child  inherits  from  its  parents,  makes  its  appearance. 
Occasionally  the  dark  hair  is  retained  for  several  weeks, 


THE   HAIR   AS  A   RUDIMENTARY   ORGAN.  207 

or  even  months,  after  birth.  This  remarkable  woolly 
covering  can  only  be  explained  as  an  inheritance  from  our 
primordial  long-haired  ancestors,  the  Apes. 

It  is  equally  worthy  of  note  that  many  of  the  higher 
Apes  resemble  Man  in  the  thin  coat  of  hair  which  covers 
certain  parts  of  their  body.  In  most  Apes,  especially  in 
the  higher  Catarhines,  the  face  is  nearly  or  even  quite  bare, 
or  is  covered  with  hairs  as  thin  and  as  short  as  those  of 
Man.  In  these  Apes  also,  just  as  in  Man,  the  hair  on  the 
back  of  the  head  is  usually  distinguished  by  its  length, 
and  the  males  often  have  much  beard  and  whisker.  (Cf. 
Fig.  202,  p.  175).  In  both  cases  this  masculine  adornment 
has  been  acquired  in  consequence  of  sexual  selection. 
In  some  Apes  the  breast  and  the  inner  sides  of  the  joints 
are  very  thinly  covered  with  hair — far  less  abundantly  than 
is  the  back  and  the  outer  sides  of  the  joints.  On  the  other 
hand,  we  not  unfrequently  see  the  shoulders,  the  back,  and 
the  outer  sides  of  the  limbs  thickly  covered  with  hair  in 
men  of  Indo-Germanic  or  Semitic  race.  It  is  a  well-known 
fact  that  in  some  families  abundant  hair  on  the  body  is 
hereditary,  as  is  the  relative  vigour  and  character  of  the 
hair-growth  of  the  beard  and  head.  These  great  differences 
in  the  total  and  partial  hairiness  of  the  body,  which  appear 
very  striking  not  only  when  we  compare  different  races  of 
man,  but  even  when  we  compare  many  families  belonging 
to  the  same  race,  are  very  simply  explained  by  the  fact 
that  the  entire  hairy  covering  of  Man  is  a  rudimentary 
organ,  an  unused  inheritance,  which  has  been  transmitted 
from  the  more  hirsute  Apes.  In  this  matter,  Man  resembles 
the  Elephant,  Rhinoceros,  Hippopotamus,  Whale,  and  other 
Mammals  of  various   orders  which    have   also    entirely  or 


208  THE   EVOLUTION   OF  MAN. 

partially  lost  their  original  coat  of  hair  in  consequence  of 
adaptation.168 

The  form  of  Adaptation  which  has  degraded  the  growth 
of  hair  on  most  parts  of  the  human  body,  while  preserving 
it,  or  even  greatly  developing  it,  on  certain  parts,  was,  in  all 
probability,  sexual  selection.  As  Darwin  has  very  clearly 
shown  in  his  work  on  "  The  Descent  of  Man,"  sexual  selec- 
tion has  had  especially  great  influence  in  this  respect.  In 
consequence  of  the  male  Anthropoid  Apes,  in  selecting  a 
partner,  preferring  those  females  which  were  least  hairy, 
and  in  consequence  of  the  females  preferring  those  suitors 
which  were  distinguished  by  peculiarly  fine  beard  or  head- 
hair,  the  general  hirsuteness  of  the  body  was  gradually 
degraded,  while  the  beard  and  the  hair  of  the  head  were 
advanced  to  a  higher  degree  of  perfection.  Climatic  con- 
ditions, and  other  circumstances  unknown  to  us,  may, 
however,  also  have  promoted  the  loss  of  the  hairy  coat. 

In  proof  of  the  assertion  that  the  hairy  covering  of 
Man  is  directly  inherited  from  the  Anthropoid  Apes,  we 
find,  according  to  Darwin,  a  curious  evidence  in  the  direc- 
tion, otherwise  inexplicable,  in  which  the  rudimentary 
hairs  lie  on  our  arms.  Both  on  the  upper  and  on  the 
lower  arm  the  hairs  are  directed  towards  the  elbow,  where 
they  meet  at  an  obtuse  angle.  Except  in  Man,  this  striking 
arrangement  occurs  only  in  the  Anthropoid  Apes,  the  Gorilla, 
Chimpanzee,  Orang,  and  several  species  of  Gibbons.  In 
other  Gibbons  the  hairs  of  both  the  lower  and  the  upper  arm 
are  directed  towards  the  hand,  as  in  other  Mammals.  This 
remarkable  peculiarity  of  Anthropoids  and  of  Man  can 
only  be  explained  on  the  assumption  that  our  common  ape- 
like ancestors   were   accustomed,  as  they   are   even  now, 


THE   NERVOUS   SYSTEM.  209 

during  rain,  to  bring  their  hands  together  over  their  heads, 
or  over  a  branch  overhanging  their  heads.  The  reverse 
direction  of  the  hairs,  when  the  arms  were  in  this  position 
caused  the  rain  to  run  off.  Thus,  even  yet,  the  direction 
of  the  hairs  on  our  lower  arm  testifies  to  this  advantageous 
habit  of  our  Ape-ancestors. 

If  the  skin  and  its  appendages  are  minutely  examined, 
Comparative  Anatomy  and  Ontogeny  supply  many  similar 
important  "  records  of  creation,"  showing  that  they  are 
directly  inherited  from  the  skin-covering  of  the  Ape.  We 
obtained  our  skin  and  hair  by  inheritance,  immediately 
from  Anthropoid  Apes,  these  from  the  lower  Apes,  which, 
in  turn,  inherited  the  same  parts  from  lower  Mammals. 
This  is  also  true  of  the  other  great  organ-system  which 
is  developed  from  the  skin-sensory  layer — of  the  nervous 
system  and  the  sensory  organs.  This  very  highly  developed 
organ  system,  which  performs  the  highest  vital  functions — 
those  of  the  mind — we  have  inherited  immediately  from 
the  Apes,  and  mediately  from  Mammals  of  a  lower  order. 

The  human  nervous  system,  like  that  of  all  other 
Mammals,  is,  in  its  developed  condition,  a  very  complex 
apparatus,  the  anatomical  arrangement  and  the  physiological 
activity  of  which  may,  in  general  terms,  be  compared  to  a 
telegraph  system.  The  central  marrow  (medulla),  or  cen- 
tral nervous  system,  represents  the  principal  station,  the  in- 
numerable "ganglion  cells"  (Fig.  7,  vol.  i.  p.  129)  of  which  are 
connected  with  each  other  and  with  numerous  very  delicate 
conducting  lines  by  their  branched  processes.  The  latter 
are  the  peripheric  "  nerve  fibres,"  distributed  over  the  whole 
surface  of  the  body ;  these,  together  with  their  terminal 
apparatus,  the  sense-organs,  etc.,  constitute  the  "  conductive 


2IO 


THE   EVOLUTION   OF   MAN. 


marrow,"  the  peripheric  nerve-system.  Some,  as  sensory 
nerve-fibres,  convey  the  sensations  of  the  skin  and  of  other 
sense-organs  to  the  central  medulla ;  others,  as  motor  nerve- 
fibres,  transmit  the  impulses  from  the  central  marrow  to  the 
muscles. 


Fig.  217. — Human  embryo 
of  three  months,  in  natural 
size,  seen  from  the  dorsal  side ; 
the  brain  and  dorsal  marrow 
exposed  (after  Koelliker)  :  h, 
hemispheres  of  the  cerebrum 
(fore-brain);  m,  "four-bulbs" 
(mid-brain)  ;  c,  small  brain 
(hind-brain,  or  cerebellum). 
Below  the  latter  is  the 
three-cornered  "neck-medulla  " 
(after-brain) . 

Fig.  218. — Central  marrow 
of  a  human  embryo  of  four 
months,  in  natural  size,  seen 
from  the  dorsal  side  (after 
Koelliker)  :  h,  large  hemi- 
spheres;  v,  "  four-bulbs  ; "  c, 
small  brain ;  mo,  neck-medulla. 
Below  this  the  dorsal  medulla 
marrow). 


The  central  nervous  system,  or  central  marrow  (medulla 
centralis),  is  the  actual  organ  of  mental  activities,  in  the 
stricter  sense.  Whatever  view  is  taken  of  the  intimate 
connection  between  this  organ  and  its  functions,  it  is,  at 
least,  certain  that  those  of  its  special  activities  which  we 
call  sensation,  volition,  and  thought,  are  in  man,  as  in  all 
the  higher  animals,  inseparably  connected  with  the  normal 
development  of  this  material  organ.  Hence  we  must  neces- 
sarily take  a  deep  interest  in  the  history  of  the  development 


THE  CENTRAL  MARROW.  211 

of  this  organ.  As  it  alone  can  give  us  the  most  important 
information  as  to  the  nature  of  our  "  mind,"  it  commands 
our  most  earnest  attention.  For  if  the  central  marrow 
develops  in  the  human  embryo  exactly  as  in  the  embryos 
of  all  other  Mammals,  then  the  development  of  the  human 
mental  organ  from  the  same  central  organ  of  other  Mammals 
and,  more  remotely,  from  that  of  lower  Vertebrates,  cannot 
be  questioned.  It  is,  therefore,  impossible  to  dispute  the 
enormous  significance  of  these  phenomena  of  development. 

In  order  to  appreciate  these  rightly,  a  few  words  must 
first  be  said  as  to  the  general  form  and  anatomical  construc- 
tion of  the  developed  central  marrow  in  Man.  Like  the 
central  nervous  system  of  all  other  Skulled  Animals  (Cra- 
niota),  it  consists  of  two  distinct  parts  :  firstly,  of  the  brain 
or  the  medulla  of  the  head  (encepfialon,  or  medulla  ca- 
pitis), and,  secondly,  of  the  spinal  marrow  (medulla  spi- 
nalis). The  former  is  enclosed  in  the  bony  skull,  or  "brain 
case,"  the  latter  in  the  bony  vertebral  canal,  which  is  com- 
posed of  a  consecutive  series  of  vertebrae,  shaped  like  signet 
rings.  (Cf.  Plate  V.  Fig.  16,  m.)  From  the  brain  proceed 
twelve  pairs  of  head  nerves,  from  the  spinal  marrow  thirty- 
one  pairs  of  medullary  or  spinal  nerves  for  the  remainder 
of  the  body.  The  spinal  marrow,  when  examined  merely 
anatomically,  appears  as  a  cylindrical  cord  with  a  spindle- 
shaped  swelling  in  the  region  of  the  neck  (at  the  last  of  the 
neck-vertebra?)  and  another  in  the  lumbar  region  (at  the 
first  lumbar  vertebra,  Figs.  217,  218).  At  the  swelling  at 
the  throat  the  large  nerves  of  the  upper  limbs  pass  off  from 
the  spinal  marrow,  and  those  of  the  lower  limbs  from  the 
swelling  in  the  lumbar  region.  The  upper  end  of  the  spinal 
marrow  passes  through  the  neck-marrow  (medulla  oblon- 


212 


THE    EVOLUTION    OF   MAN. 


gata)  into  the  brain.  The  spinal  marrow  appears  indeed  to 
be  a  dense  mass  of  nervous  substance ;  but  along  its  axis 
passes  a  very  narrow  canal,  which  is  continued  in  front 
into  the  larger  cavities  of  the  brain,  and  which,  like  those 
cavities,  is  filled  with  a  clear  fluid. 

The  brain  forms  a  considerable  mass  of  nervous  sub- 
stance, of  very  complex,  minute  structure,  which  occupies 


Fig.  219. — Human  brain, 
seen  from  the  lower  side. 
(After  H.  Meyer.)  Above  (in 
front)  is  the  large  brain 
(cerebrum),  with  extensively 
branched  furrows  ;  below  (be- 
hind) is  the  small  brain  (cere- 
bellum), with  narrow  parallel 
furrows.  The  Roman  numbers 
indicate  the  roots  of  the  twelve 
pairs  of  brain  nerves  in  order 
from  froLt  to  back. 


the  greater  part  of  the  skull-cavity ;  it  is  roughly  distin- 
guishable into  two  main  parts — the  large  and  small  brain 
(cerebrum  and  cerebellum).  The  former  is  situated  in 
front  and  over  the  latter,  and  its  surface  exhibits  the  well- 
known  characteristic  convolutions  and  furrows  (Figs.  219, 
220).  On  its  upper  surface  it  is  divided  by  a  deep  longi- 
tudinal slit  into  two  lateral  halves,  the  so-called  "great 
hemispheres,"  which  are  connected  by  means  of  a  bridge,  or 
"  cross-piece  "  {corpus  callosum).  A  deep  transverse  fissure 
separates  the  large  brain  (cerebrum)  from  the  small  brain 


THE   BRAIN. 


213 


(cerebellum).  The  latter  is  situated  more  posteriorly  and 
inferiorly,  and  shows  on  its  outer  surface  equally  numerous 
furrows,  which  are,  however,  much  finer  and  more  regular, 


Fig.  220. — Human  brain,  seen  from  the  left  side.  (After  H.  Meyer.)  The 
furrows  of  the  large  brain  are  indicated  by  large,  thick  lines,  those  of  the 
small  brain  by  finer  lines.  Below  the  latter  the  neck-marrow  is  visible.  fl-f3, 
frontal  convolutions  ;  Ce.  a  Ce.  p,  central  convolutions  ;  B,  fissure  of  Bolan- 
dus;  S,  Sylvian  fissure;  T,  temporal  or  parallel  fissure;  Pa,  parietal  lobe;  An, 
the  annectant  convolutions  ;  PO,  parieto-occipital  fissure  ;  Su,  supra-marginal 
convolution;  IP,  intra-parietal  fissure;  t,  temporo-sphenoidal  convolution. 

and  between  them  are  curved  ridges  (Fig.  219,  lower  part). 
The  small  brain  is  also  divided  into  two  lateral  halves  by  a 
longitudinal  furrow ;  these  are  the  "  small  hemispheres," 
which  are  connected  at  the  top  by  a  worm-like  cross-piece, 
the  "  brain- worm  "  (vermis),  and  at  the  bottom  by  a  bridge 
(pons  varolii;  Fig.  219,  VI.). 

Comparative  Anatomy  and  Ontogeny  show,  however,  that 
in  .Man,  as  in  all  other  Skulled  Animals,  the  brain  originally 
consists  not  of  two  but  of  five  distinct  parts  lying  one 
behind  another.    These  originally  appear  in  the  embryo  of  all 


214  THE   EVOLUTION   OF   MAN. 

Skulled  Animals  (Craniota),  from  the  Cyclostomi  and  Fishes 
up  to  Man,  in  exactly  the  same  form,  as  five  bladders 
placed  one  behind  the  other.  Alike  in  their  first  rudiments, 
they,  however,  differ  in  their  further  development.  In  Man 
and  all  higher  Mammals  the  first  of  these  five  bladders,  the 
fore-brain,  develops  so  excessively  that,  when  mature,  it 
forms,  both  in  size  and  weight,  by  far  the  greater  part  of  the 
whole  brain.  To  it  belong,  not  only  the  great  hemispheres, 
but  also  the  bridge  (corpus  callosum),  which  connects  these 
two,  the  olfactory  lobes,  from  which  proceed  the  nerves  of 
smell,  and  most  of  the  processes  lying  on  the  roof  and  floor 
of  the  great  lateral  cavities  of  the  two  hemispheres ;  such, 
for  instance,  as  the  large  streaked  bodies  (corpora  striata). 
On  the  other  hand,  the  "  centres  of  sight,"  which  lie  be- 
tween the  streaked  bodies,  belong  to  the  second  main  part, 
which  develops  from  the  twixt-brain ;  and  to  the  same  part 
belong  the  third  brain  ventricle  (which  is  single)  and  the 
processes  known  as  the  "funnel"  (infandibulum),  the 
gray  mass,  and  the  "  cone  "  (conarium).  Behind  these,  and 
between  the  large  brain  and  the  small  brain,  we  find  a  little 
mass,  composed  of  two  pairs  of  bosses,  and  called  the  "  four 
bulbs,"  on  account  of  two  superficial  furrows  which  cross 
each  other  at  right  angles,  thus  quartering  the  whole  mass 
(Figs.  217,  m,  218,  v).  Though  these  "  four  bulbs"  are  very 
insignificant  in  Man  and  the  higher  Mammalia,  they 
constitute  a  distinct  part  of  the  brain,  the  third,  or  mid- 
brain, which  is,  on  the  contrary,  especially  well  developed 
in  the  lower  Vertebrates.  The  next  or  fourth  part  of  the 
brain  is  the  hind-brain,  or  small  brain  (cerebellum),  in  the 
strict  sense  of  the  term,  with  its  single  middle  process, 
the  "  worm  "  (vermis),  and  its  two  lateral  parts,  the  "  small 


PARTS   OF   THE   BRAIN.  215 

hemispheres"  (Figs.  217,  c,  218,  c).  Behind  this  comes,  finally, 
the  fifth  and  last  part,  the  "  neck-marrow  "  (medulla  oblon- 
<j<da,  Fig.  218,  mo),  which  includes  the  single  fourth  brain 
ventricle  and  the  adjoining  processes  (pyramids,  olives,  and 
restiform  bodies).  The  neck  medulla  passes  directly  down 
into  the  spinal  marrow.  The  narrow  central  canal  of  the 
spinal  marrow  extends  into  the  wider  "  fourth  ventricle  "  of 
the  neck  medulla,  which  is  rhomboidal  in  shape,  and  the 
floor  of  which  forms  the  "rhomboid  groove."  From  this 
proceeds  a  narrow  duct,  called  the  "  aqueduct  of  Sylvius," 
which  leads  through  the  "  four-bulbs  "  into  the  third  ven- 
tricle, situated  between  the  two  "  centres  of  sight ; "  and 
this  cavity  in  turn  is  connected  with  the  pair  of  lateral 
cavities  which  lie  right  and  left  in  the  large  hemispheres. 
All  the  cavities  of  the  central  marrow  are,  therefore,  directly 
connected  together.  Individually  all  these  parts  of  the  brain 
which  we  have  enumerated  have  an  infinitely  complex, 
minute  structure,  which  we  cannot  now  study,  and  which 
hardly  bears  on  our  subject.  This  wonderful  brain-struc- 
ture, as  it  occurs  only  in  Man  and  the  higher  Vertebrates,  is 
of  the  highest  importance,  simply  because,  in  all  Skulled 
Animals  (Craniota),  it  develops  from  the  same  simple  rudi- 
ments, from  the  five  brain-bladders  already  enumerated. 
(Cf.  Plates  VI.  and  VII.) 

Before  we  direct  our  attention  to  the  individual  develop- 
ment of  the  complex  brain  from  this  series  of  simple 
bladders,  we  will,  in  order  to  understand  the  matter  more 
clearly,  glance  for  a  moment  at  those  lower  animals  which 
have  no  such  brain.  Even  in  the  skull-less  Vertebrates,  in 
the  Amphioxus,  there  is  no  real  brain.  In  this  case  the 
whole  central  marrow  is  merely  a  simple  cylindrical  cord 


2l6  THE   EVOLUTION   OF  MAN. 

traversing  the  body  longitudinally,  and  terminating  in  front 
almost  as  simply  as  at  the  other  end :  it  is  a  simple  medul- 
lary tube  (Plate  XI.  Fig.  15,  m).  We  found,  however,  that 
the  rudiment  of  the  same  simple  medullary  tube  occurs  in 
the  ascidian  larva  (Plate  X.  Fig.  5,  m)  and  in  the  same  cha- 
racteristic position,  above  the  notochord.  Moreover,  when 
closely  examined  a  small  bladder-like  swelling  may  be  seen 
at  the  fore  end  of  the  medullary  tube  in  these  two  closely 
allied  animals  ;  this  is  the  first  indication  of  a  separation  of 
the  medullary  tube  into  brain  (m^  and  spinal  marrow  (m2). 
When,  however,  we  consider  the  undeniable  relationship  of 
the  Ascidia  to  the  rest  of  the  Worms,  it  is  evident  that  the 
simple  central  marrow  of  the  former  exactly  answers  to  the 
simple  nerve-ganglion  which,  in  the  lower  Worms  lies  above 
the  throat  {'pharynx),  and  which  has,  therefore,  long  been 
called  the  "  upper  throat  ganglion  "  {ganglion  pharyngeum 
super ius).  In  the  Gliding  Worms  (Turbellaria)  the  whole 
nerve  system  consists  merely  of  this  simple  ganglion,  which  is 
situated  on  the  dorsal  side  of  the  body,  and  from  which  nerve- 
threads  radiate  to  the  different  parts  of  the  body  (Fig.  211, gri) 
This  upper  throat  ganglion  of  the  lower  Worms  is  evidently 
the  rudiment  from  which  the  more  complex  central  marrow 
of  the  higher  animals  has  developed.  An  elongation  of  the 
upper  throat  ganglion  along  the  dorsal  side  gave  rise  to 
the  medullary  tube,  which  is  characteristic  of  Vertebrates 
and  the  young  forms  of  Ascidia  alone.  On  the  other  hand, 
in  all  other  animals,  the  central  nerve  system  has  de- 
veloped in  a  very  different  manner  from  the  upper  throat 
ganglion;  in  Articulated  Animals  {Arthropoda)  especially, 
the  latter  has  developed  into  a  throat  (pharyngeal)  ring, 
with  a  ventral  marrow ;  this  is  the  case,  also,  in  the  articu- 


THE   NERVOUS   SYSTEM   IN   THE   LOWER  ANIMALS.        2\J 

latecl  Ringed  Worms  (Annelida)  and  the  Star-animals  (Ecki- 
noderma),  which  originated  from  Arthropods.  The  Soft- 
bodied  Animals  (Mollusca)  also  have  a  throat  ring,  which  is 
quite  unrepresented  in  Vertebrates.  Only  in  Vertebrates 
the  central  marrow  developed  along  the  dorsal  side,  while 
in  all  other  animals  which  have  been  named  it  developed 
along  the  ventral  side  of  the  body.169 

Descending  below  the  Worms  we  find  very  many 
animals  which  are  entirely  without  a  nerve-system,  and  in 
which  the  functions  of  that  system  are  performed  simply  by 
the  outer  skin-covering — by  the  cells  of  the  skin-layer,  or 
exoderm.  This  is  the  case  in  many  low  Plant  Animals 
(Zoophyta),  for  instance,  in  all  Sponges,  and  in  the  common 
fresh-water  Polyp,  the  Hydra.  It  was  also  undoubtedly  the 
case  in  all  extinct  Gastrseads.  In  all  Primitive  Animals 
(Protozoa)  the  nerve-system  is,  of  course,  unrepresented,  for 
these  have  not  as  yet  attained  to  the  development  of  germ- 
layers. 

In  considering  the  individual  development  of  the  nerve- 
system  in  the  human  embryo,  we  must  first  of  all  start  from 
the  important  fact  already  mentioned,  that  the  first  rudi- 
ment of  the  system  is  the  simple  medullary  tube,  which 
detaches  itself  from  the  outer  germ-layer  along  the  middle 
line  of  the  lyre-shaped  primitive  germ.  We  found  (Figs. 
85-87,  vol.  i.  p.  298)  that  the  rectilineal  primitive  groove,  or 
dorsal  furrow,  first  arises  in  the  centre  of  the  lyre-shaped 
germ- disc.  On  each  side  of  this  rise  the  two  parallel  dorsal 
or  medullary  swellings.  The  free  margins  of  these  bend  to- 
wards each  other,  coalesce,  and  form  the  closed  medullary  tube 
(Figs.  88-93, vol.  i.  pp.  300-309).  At  first  this  tube  lies  directly 
under   the  horn-plate ;    it   is,  however,  afterwards  situate 


218 


THE   EVOLUTION   OF   MAN. 


■#*I^?V 


•fi!*  ^  I        . »' 


.  — ^ 


my  ■-i-7*>- 


>-■ 


X>#  NfiVi^' 

Figs.  221-223. —  Lyre-shaped  (or  sole-shaped)  germ-shield  of  a  Chick,  in 
three  consecutive  stages  of  evolution,  seen  from  the  dorsal  surface :  about 
twenty  times  enlarged.  Fig.  221,  with  six  pairs  of  primitive  vertebras. 
The  brain  a  simple  bladder  (/ib).  The  medullary  furrow  is  wide  open  from 
the  point  x,  very  wide  at  z.  mp,  Marrow  (or  medullary)  plates  ;  sp,  side- 
plates  ;  y,  boundary  between  the  throat  cavity  (sh)  and  the  head-intestine 
(vd).  Fig.  222,  with  ten  pairs  of  primitive  vertebras.  The  brain  consists  of 
three  bladders :  v,  fore-brain ;  m,  mid-brain  ;  h,  hind-brain,  c,  Heart  ;  dv, 
yelk-veins.  The  medullary  furrow  is  wide  open  behind  (s).  mp,  Marrow- 
plates.  Fig.  223,  with  sixteen  pairs  of  primitive  vertebra?.  The  brain 
consists  of  five  bladders  :  v,  fore-brain ;  z,  twixt-brain ;  m,  mid-brain ;  h, 
hind-brain  ;  n,  after-brain,  a,  Eye-vesicles  ;  g,  ear- vesicles  ;  c,  heart ;  dv, 
yelk-veins  ;  mp,  marrow-plate,    uw,  primitive  vertebras. 


DEVELOPMENT   OF   THE   BRAIN.  219 

quite  internally,  the  upper  edges  of  the  primitive  vertebral 
plates,  which  penetrate,  from  right  and  left,  in  between  the 
horn-plate  and  the  medullary  tube,  uniting  above  the  latter, 
and  thus  completely  embedding  it  in  a  closed  canal.  As 
Gegenbaur  most  aptly  remarks,  "  This  gradual  embedding 
in  the  interior  of  the  body  must  be  regarded  as  an  incident 
acquired  in  connection  with  progressive  differentiation,  and 
with  the  consequent  higher  capacity,  by  which  the  most 
important  organ  of  the  system  is  secured  in  its  interior." 

To  every  thoughtful  and  unprejudiced  man  it  must 
appear  an  extremely  important  and  pregnant  fact,  that  our 
mental  organ,  like  that  of  all  other  Skulled  Animals  (Cra- 
niota),  commences  in  the  same  way  and  in  exactly  the  same 
simple  form  in  which  this  organ  remains  for  life  in  the 
lowest  Vertebrate,  the  Amphioxus  (vol.  i.  p.  420,  Fig.  151; 
Plate  XI.  Fig.  15,  m).  In  the  C3^clostomi,  that  is,  in  the  stage 
above  the  Acrania,  the  anterior  extremity  of  the  cylindrical 
medullary  tube  begins  to  extend,  at  an  early  period,  in  the 
form  of  a  pear-shaped  bladder,  which  is  the  first  distinct 
rudiment  of  a  brain  (Plate  XL  Fig.  1G,  m,).  For  the  central 
medulla  of  Vertebrates  thus  first  distinctly  differentiates 
into  its  two  main  sections,  the  brain  (m^  and  the  spinal 
marrow  (m2).  The  first  faint  indication  of  this  important 
differentiation  is  discoverable  in  the  Amphioxus,  perhaps 
even  in  the  Ascidian  larva  (Plate  X.  Fig.  5). 

The  simple  bladder-like  form  of  the  brain,  which  is 
retained  for  a  considerable  time  in  the  Cyclostomi,  also 
appears  at  first  in  all  higher  Vertebrates  (Fig.  221,  Jib).  In 
the  latter,  however,  it  soon  disappears,  in  consequence  of 
the  separation  of  the  simple  brain-bladder,  by  transverse 
contractions  of  its  circumference,  into  several   consecutive 


220  THE   EVOLUTION   OF   MAN. 

parts.  Two  of  these  contractions  first  appear,  and  con- 
sequently the  brain  forms  three  consecutive  bladders  (Fig. 

3  *■■  *  Figs.  224-226.— Central  mar- 

row of  human  embryo  in  the 
seventh  week,  two  cm.  long. 
(After  Koelliker.)  Fig.  226, 
view  of  the  whole  embryo  from 
the  dorsal  side ;  the  brain  and 
dorsal  marrow  laid  bare.  Fig. 
225,  the  brain  and  upper  part 
of  the  dorsal  marrow  from  the 

left  side.     Fig.  224,   the  brain  from  above  :  v,  fore-brain ;  a,  twixt-brain  ; 

m  mid-brain;  h,  hind-brain  ;  n,  after-brain. 

222,  v,  rn,  h).  The  first  and  third  of  these  three  primitive 
bladders  then  again  separate  by  transverse  contractions, 
each  into  two  parts,  and  thus  five  consecutive  bladder-like 
divisions  are  formed  (Fig.  223 :  cf.  also  Plate  V.  Figs. 
13-16  ;  Plates  VI.  and  VII.,  second  cross-line).  These  five 
fundamental  brain-bladders,  which  re-occur  in  the  same  form 
in  the  embryos  of  all  the  Skulled  Animals  (Craniota),  were 
first  clearly  recognized  by  Baer,  who  understood  their  true 
importance  and  distinguished  them,  according  to  their  rela- 
tive positions,  by  very  appropriate  names,  which  are  still  in 
general  use  :  I.,  fore-brain  (v) ;  II.,  twixt-brain  (z);  III.,  mid- 
brain (m) ;  IV.,  hind-brain  (h) ,  and  V.,  after-brain  (n). 

In  all  Skulled  Animals,  from  the  Cyclostomi  to  Man, 
the  same  parts,  although  in  very  various  forms,  develop 
from  these  five  original  brain-bladders.  The  first  bladder, 
the  fore-brain  (protopsyche,  v),  forms  by  far  the  largest  part 
of  the  so-called  "great  brain  "  (cerebrum,) ;  it  forms  the  two 
great  hemispheres,  the  olfactory  lobes,  the  streaked  bodies 
(corpora  striata),  and  the  cross-piece  (corpus  callosum), 
together   with    the   "  arch "   (fornix).      From   the  second 


THE   BRAIN   IN    SKULLED   ANIMALS.  221 

bladder,  the  twixt-brain  (deutopsyche,  z,)  proceed  primarily 
the  "  centres  of  sight "  and  the  other  parts  which  surround 
the  so-called  "  third  brain-ventricle,"  also  the  "  funnel " 
(infuiuUbidum),  the  "cone"  (conarium),  etc.  The  third 
bladder,  the  mid-brain  (mesopsyche,  m),  furnishes  the  small 
group  of  the  "  four  bulbs,"  together  with  the  "  aqueduct  of 
Sylvius."  From  the  fourth  bladder,  the  hind-brain  (meta- 
psyche,  h),  the  greater  part  of  the  so-called  "  little  brain  " 
(cerebellum)  develops;  the  central  "worm"  (vermis),  and 
the  two  lateral  "small  hemispheres."  The  fifth  bladder, 
finally,  the  after-brain  (epipsyche,  n),  forms  the  neck- 
marrow,  or  the  "elongated  marrow"  (medulla  oblongata), 
together  with  the  rhomboid  groove,  the  pyramids,  olives,  etc. 
The  very  highest  importance  must  certainly  be  ascribed 
to  the  fact,  seen  in  Comparative  Anatomy  and  Ontogeny, 
that  the  brain  is  originally  formed  in  exactly  the  same  way 
in  the  embryos  of  all  Skulled  Animals  (Craniota),  from  the 
lowest  Cyclostomi  and  Fishes,  to  Apes  and  Man.  In  all, 
the  first  rudiment  of  the  brain  is  a  simple  bladder-like 
expansion  at  the  anterior  extremity  of  the  medullary  tube. 
In  all,  the  five  bladders  are  formed  from  this  simple  bladder- 
like expansion,  and  in  all,  these  five  primitive  brain- 
bladders  develop  into  the  permanent  brain,  with  its  many 
c< unplex  anatomical  arrangements,  which  afterwards  appear 
in  such  extremely  diverse  forms  in  the  various  vertebrate 
classes.  On  comparing  the  mature  brain  of  a  Fish,  an 
Amphibian,  a  Reptile,  a  Bird,  and  a  Mammal,  it  is  hardly 
conceivable  that  the  several  parts  of  these  forms,  so  ex- 
tremely different,  both  internally  and  externally,  may  be 
traced  back  to  one  common  condition.  And  yet,  all  these 
various  brains  of  Craniota  have  originated  from  exactly  the 


222 


THE   EVOLUTION    OF   MAN. 


same  rudimentary  form.  We  need  only  compare  the  em- 
bryos of  these  various  classes  of  animals  at  corresponding 
stages  of  development,  in  order  to  assure  ourselves  of  this 
fundamental  fact.  (Cf.  Plates  VI.  and  VII.,  second  cross- 
line.) 


Fig.  227. — Brains  of  three  embryonic  Skulled  Animals  in  vertical  longi- 
tudinal sections:  A,  of  a  Shark  (Heptanchus) ;  B,  of  a  Snake  (Coluber);  C,  of 
a  Goat  (Capra) ;  a,  fore-brain  ;  b,  twixt-brain  ;  c,  mid- brain  ;  d,  hind-brain  ; 
e,  after- brain;  s,  primitive  fissure  of  the  brain.      (After  Gegenbanr.) 

Fig.  228. — Brain  of  a  Shark  (Scyllium)  from  the  dorsal  side :  g,  fore- 
brain  ;  h,  olfactory  bulbs  of  the  fore-brain,  which  send  the  large  olfactory 
nerves  to  the  large  nose  capsules  (o) ;  d,  twixt-brain ;  b,  mid-brain  (behind 
it,  the  insignificant  rudiment  of  the  hind-brain) ;  a,  after-bi'ain.  (After 
Busch.) 

Fig.  229. — Brain  and  dorsal  marrow  of  a  Frog  :  A,  from  the  dorsal  side  ; 
B,  from  the  ventral  side ;  o,  olfactory  bulbs,  in  front  of  the  fore-brain  (b) ; 
i,  funnel  at  the  base  of  the  twixt-brain ;  c,  mid-brain ;  d,  hind-brain ;  s, 
rhomboid  groove  in  the  after-brain  ;  m,  dorsal  marrow  (very  short  in  the 
frog) ;  m',  root-processes  of  the  spinal  nerves ;  t,  fibre  at  the  end  of  the 
dorsal  marrow.      (After  Gegenbaur.) 


COMPARATIVE   VIEW   OF   BRAIN   DEVELOPMENT.         22$ 

A  thorough  comparison  of  the  corresponding  stages  of 
development  in  the  brain  in  the  various  Skulled  Animals 
(Craniota)  is  very  instructive.  If  it  is  applied  to  the  whole 
series  of  skulled  classes,  the  following  extremely  interest- 
ing facts  soon  become  evident :  in  the  Cyclostomi  (Myxi- 
noides  and  Petromyzontcs),  which,  as  we  have  seen,  are 
the  lowest  and  earliest  Skulled  Animals,  the  whole  brain 
remains  for  life  at  a  very  low  and  primitive  stage  of 
development,  through  which  the  embryos  of  the  other 
Skulled  Animals  pass  very  rapidly;  the  five  original 
sections  of  the  brain  are  visible  throughout  life  in  an  almost 
unmodified  form.  But  even  in  Fishes,  an  essential  and 
important  transformation  of  the  five  bladders  takes  place ; 
it  is  evidently  from  the  brain  of  the  Primitive  Fishes 
(Selachii ;  Fig.  228),  that,  on  the  one  side,  the  brain  of  the 
other  Fishes,  and  on  the  other,  the  brain  of  the  Amphibians 
and  also  of  the  higher  Vertebrates,  must  be  traced.  In 
Fishes  and  Amphibians  (Fig.  220),  the  central  part,  the 
mid-brain,  and  also  the  fifth  section,  the  after-brain,  are 
especially  developed,  while  the  first,  second,  and  fourth 
sections  remain  far  behind.  In  the  higher  Vertebrates,  the 
exact  reverse  is  the  case,  for  in  these  the  first  and  fourth 
sections,  the  fore  and  hind  brains,  develop  pre-eminently ;  on 
the  other  hand,  the  mid-brain  remains  very  small,  and  the 
after-brain  is  also  much  smaller.  The  greater  part  of  the 
"  four-bulbs "  is  covered  by  the  large  brain  (ccrebruwi)  and 
the  after-brain  by  the  small  brain  (cerebellum).  Even 
among  the  higher  Vertebrates  themselves,  numerous  grada- 
tions occur  in  the  structure  of  the  brain.  From  the  Am- 
phibians upward,  the  brain,  and  with  it  the  mental  life, 
develops  in  two  different  directions,  of  which  the  one  is 
33 


224 


THE   EVOLUTION   OF   MAN. 


carried  out  in  Keptiles  and  Birds,  the  other  in  Mammals. 
The  latter  are  especially  distinguished  by  the  very  charac- 
teristic development  of  the  first  section,  the  fore-brain.     In 


Fig.  230. — Brain  of  Eabbit :  A,  from  the  dorsal  side ;  B,  from  the 
ventral  side ;  lo,  olfactory  lobnles  ;  I.,  fore-brain  ;  h,  hypophysis  at  the  base 
of  the  twixt-brain  ;  III.,  mid- brain  ;  IV.,  hind-brain;  V.,  after-brain;  2,  optic 
nerve ;  3,  motor  nerve  of  the  eye ;  5-8,  fifth  to  eighth  nerves  of  the  brain. 
In  A,  the  npper  surface  of  the  right  large  hemisphere  (I.)  is  removed,  so 
that  the  streaked  bodies  (corpora  striata)  can  be  seen  in  its  side  chamber 
(yentriculus  lateralis).     (After  Gegenbaur.) 

Mammals  alone  (Fig.  230)  does  this  "great  brain"  develop 
to  such  an  extent,  that  it  eventually  covers  all  the  other 
parts  of  the  brain  from  above. 

There  are  also  remarkable  differences  in  the  relative 
positions  of  the  brain-bladders.  In  the  lower  Skulled 
Animals  the  five  brain-bladders  are  at  first  situated  one 
behind  the  other  in  the  same  plane.  If  the  brain  is  re- 
garded from  the  side,  a  straight  line  may  be  drawn  through 
all  the  five  bladders.  But  in  the  three  higher  vertebrate 
classes,  in  the  Amnion  Animals  (Amniota),  a  noticeable 
curving  of  the  rudimentary  brain  takes  place,  simultaneously 


BRAIN   CURVATURE.  225 

with  the  head  and  neck  curving  of  the  whole  body,  owing 
to  the  fact  that  the  whole  upper  dorsal  surface  of  the  brain 
grows  much  faster  than  the  lower  ventral  surface.  The 
result  is  that  the  brain  is  so  curved  that  its  parts  are  after- 
wards situated  thus :  the  fore-brain  lies  quite  in  front  and 
below,  the  twixt-brain  somewhat  higher  and  over  it,  while 
the  mid-brain  lies  highest  of  all  and  projects  furthest  for- 
ward; the  hind-brain  is  situated  lower,  the  after-brain  yet 
further  back  and  below.  This  disposition  occurs  only  in 
the  three  classes  of  the  Amniota,  in  Reptiles,  Birds,  and 
Mammals.     (Cf.  Plates  I.,  VI.,  and  VII.) 

Though,  in  general  features  of  growth,  the  brains  of 
Mammals  correspond  with  those  of  Birds  and  Reptiles,  yet 
striking  differences  very  soon  appear  between  the  two. 
In  Birds  and  Reptiles  (Plate  VI.  Figs.  H  and  G),  the  mid- 
brain (m)  and  the  central  part  of  the  hind-brain  develop 
considerably.  In  Mammals,  on  the  other  hand,  these  parts 
remain  small,  and  instead,  the  fore-brain  begins  to  grow 
so  rapidly  that  it  covers  the  other  bladders  from  in  front 
and  above.  As  it  constantly  grows  further  back,  it  even- 
tually covers  the  whole  of  the  rest  of  the  brain  above, 
and  also  encloses  the  central  part  from  the  sides.  This 
process  is  of  the  greatest  importance,  because  this  fore-brain 
is  the  organ  of  the  higher  mental  activities, — because  in  it 
are  accomplished  those  functions  of  the  nerve-cells,  the  sum 
of  which  is  generally  designated  as  the  mind,  or  the  "spirit" 
in  the  narrower  sense.  The  highest  activities  of  the  animal 
body,  the  wonderful  manifestations  of  consciousness,  the 
complex  phenomena  of  the  activities  of  thought,  have  their 
seat  in  the  fore-brain.  It  is  possible  to  remove  the  great 
hemispheres  of  a  Mammal,  piece  by  piece,  without  killing 


226  THE   EVOLUTION   OF   MAN. 

the  animal,  thus  proving  that  the  higher  mental  activities, 
consciousness  and  thought,  conscious  volition  and  sensation, 
may  be  destroyed  one  by  one,  and  finally  entirely  anni- 
hilated. If  the  animal  thus  treated  is  artificially  fed,  it 
may  be  kept  alive  for  a  long  time ;  for  the  nourishment  of 
the  entire  body,  digestion,  respiration,  the  circulation  of  the 
blood,  secretion,  in  short,  the  vegetative  functions,  are  in 
no  way  destroyed  by  this  destruction  of  the  most  important 
mental  organs.  Conscious  sensation  and  voluntary  motion, 
the  capacity  for  thought  and  the  combination  of  the  various 
higher  mental  activities,  have  alone  been  lost. 

This  fore-brain,  the  source  of  all  these  most  wonderful 
nervous  activities,  reaches  that  high  degree  of  perfection  only 
in  the  higher  Placental  Animals  {Placentalia) ;  a  fact  which 
explains  very  clearly  why  the  higher  Mammals  so  far  excel 
the  lower  in  intellectual  capacity.  While  the  "mind"  of  the 
lower  Placental  Animals  does  not  exceed  that  of  Birds  and 
Reptiles,  we  find  among  the  higher  Placentalia  an  uninter- 
rupted gradation  up  to  Apes  and  Man.  Accordingly,  their 
anterior  brains  show  surprising  differences  in  the  degree  of 
perfection.  In  the  lower  Mammals,  the  surface  of  the  great 
hemispheres  (the  most  important  part)  is  entirely  smooth 
and  even.  The  fore -brain,  too,  remains  so  small  that  it 
does  not  even  cover  the  mid-brain  above  (Fig.  230).  One 
stage  higher,  and  this  latter  is  indeed  entirely  covered  by 
the  excessive  growth  of  the  fore-brain ;  but  the  hind-brain 
remains  free  and  uncovered.  At  last,  in  Apes  and  in  Man, 
the  fore-brain  covers  the  hind-brain  also.  A  similar  gradual 
advance  may  also  be  traced  in  the  development  of  the 
peculiar  furrows  and  protuberances  which  are  so  charac- 
teristically prominent  on   the  surface   of  the   large  brain 


CONVOLUTIONS   OF    BRAIN.  227 

(cerebrum)  of  higher  Mammals  (Figs.  219,  220).  If  the 
brains  of  the  various  mammalian  groups  are  compared  with 
reference  to  these  convolutions  and  furrows,  it  appears  that 
their  gradual  development  is  entirely  proportionate  with 
the  development  of  the  higher  intellectual  activities.  Much 
attention  has  recently  been  devoted  to  this  particular 
branch  of  the  Anatomy  of  the  brain,  and  very  striking 
individual  differences  have  been  found  even  within  the 
human  race.  In  all  human  individuals  distinguished  by 
peculiar  ability  and  great  intellect,  these  swellings  and 
furrows  on  the  surface  of  the  great  hemispheres  exhibit  a 
much  greater  development  than  in  common  average  men; 
while  in  the  latter,  again,  they  are  more  developed  than  in 
Cretins  and  others  of  unusually  feeble  intellect.  There  are 
also  similar  gradations  in  the  internal  structure  of  the  fore- 
brain  in  Mammals.  The  great  cross-piece  {corpus  callosum), 
especially,  the  bridge  between  the  two  great  hemispheres, 
is  developed  only  in  Placental  Animals.  Other  arrange- 
ments, for  example,  in  the  structure  of  the  lateral  cavities, 
which  seem  primarily  to  be  peculiar  to  Men  as  such,  re- 
appear only  in  the  higher  species  of  Apes.  It  was  long- 
believed  that  Man  had  some  entirely  peculiar  organs  in  the 
great  brain  (cerebrum),  which  are  wanting  in  all  other  animals. 
But  close  comparison  has  shown  that  this  is  not  the  case, 
but  that  rather  the  characteristic  qualities  of  the  human 
brain  exist  in  a  rudimentary  state  even  in  the  lower  Apes, 
and  are  developed  to  a  greater  or  less  degree  in  the  higher 
Apes.  Huxley,  in  his  important  and  much-quoted  book, 
"  Evidence  as  to  Man's  Place  in  Nature  "  (18G3),  has  shown, 
most  convincingly,  that  within  the  Ape-series  the  differences 
in    the   formation   of  the   brain   are    greater   between  the 


228  THE   EVOLUTION   OF   MAN. 

higher  and  lower  Apes  than  between  the  higher  Apes  and 
Man.  This  statement  is,  indeed,  equally  true  of  all  the 
other  parts  of  the  body.  But  the  fact  that  it  is  true  of  the 
central  marrow  is  especially  important.  This  does  not 
become  fully  evident  unless  these  morphological  facts  are 
considered  in  connection  with  the  corresponding  physio- 
logical phenomena;  until  we  consider  that  every  mental 
activity  requires  for  its  complete  and  normal  exercise  the 
complete  and  normal  condition  of  the  corresponding  brain- 
structure.  The  extremely  complex  and  perfect  active 
phenomena  within  the  nerve-cells,  summed  up  in  the  word 
"mental  life,"  can  no  more  exist  without  their  organs  in 
the  vertebrates,  including  man,  than  can  the  circulation  of 
the  blood  without  a  heart  or  blood.  As,  however,  the 
central  marrow  of  Man  has  developed  from  the  same 
medullary  tube  as  in  all  other  Vertebrates,  so  also  must  the 
mental  life  of  Man  have  had  the  same  origin. 

All  this  is  of  course  true  of  the  conductive  marrow,  or 
the  so-called  "peripheric  nervous  system."  This  consists 
of  the  sensitive  nervous  fibres  which  convey  the  impressions 
of  sensation  from  the  skin  and  the  organs  of  the  senses  in 
a  centripetal  direction  to  the  central  marrow ;  as  well  as 
of  the  motor  nervous  fibres,  which,  reversely,  convey  the 
movements  of  volition  from  the  central  marrow,  in  a  cen- 
trifugal direction  to  the  muscles.  By  far  the  greater  part 
of  these  peripheric  conductive  nerves  originates  from  the 
skin-fibrous  layer,  by  peculiar  local  differentiation  of  the 
rows  of  cells  into  the  respective  organs. 

The  membranous  coverings  and  blood-vessels  of  the 
central  marrow  are  identical  in  origin  with  the  greater  part 
of  the  conductive   marrow;    these  membranous  coverings 


ORIGIN   OF   THE   FUNCTIONS   OF   THE  BRAIN.  229 

are  the  inner  membrane  (pia  mater),  the  central  membrane 
(meninx  arachnoides),  and  the  outer  membrane  (dura 
mater).  All  these  parts  are  developed  from  the  skin-fibrous 
layer. 


TABLE   XXVII. 

Systematic  Survey  of  the  most  important  Periods  in  the  Fhylogeny 
of  the  Human  Skin-coverings. 

I.  First  Period  :  Skin  of  Castr&ads. 

The  entire  skin-covering  (including  the  nervous  system,  not  yet  differ- 
entiated from  it)  consists  of  one  simple  layer  of  ciliated  cells  (exoderm,  or 
primary-  skin-layer);  as  it  is  at  the  present  day  in  the  gastrula  of  the 
Amphioxus. 

II.  Second  Period  :  Skin  of  Primitive  TT'orms. 

The  simple  exoderm  of  the  Gastrsead  has  thickened  and  split  into  two 
distinct  layers,  or  secondary  germ-layers  :  the  skin-sensory  layer  (rudiment 
of  the  horn-plate  and  nerve-system)  and  the  skin-fibrous  layer  (rudiment  of 
the  leather  skin  (corium),  the  muscle-plate  and  the  skeleton-plate.  The 
skin  is  potentially  both  covering  and  mind. 

III.   Third  Period  :  Skin  of  Chordoma. 

The  skin-sensory  layer  has  differentiated  into  the  horn-plate  (epidermis), 
and  the  central  marrow  (upper  throat  ganglia)  separated  from  it ;  the  latter 
elongates  into  a  medullary  tube.  The  skin-fibrous  layer  has  differentiated 
into  the  leather  plate  (corium)  and,  below  this,  the  skin-muscular  pouch  (as 
in  all  Worms). 

IV.  Fourth  Period  :  Skin  of  Acrania. 

The  horn-plate  yet  forms  a  simple  epidermis.  The  leather-plate  is  fully 
differentiated  from  the  muscle  and  skeleton  plates. 


230  THE   EVOLUTION   OF  MAN. 

V.  Fifth  Period  :  Skin  of  Cyclostoma. 

The  outer-skin  remains  a  simple,  soft  mucous  layer  of  cells,  but  forms 
one-celled  glands  (cup-cells).  The  leather-skin  (corium)  differentiates  into 
cutis  and  sub-culis. 

VI.  Sixth  Period  :  Skin  of  Primitive  Fishes. 

The  outer  skin  is  still  simple.  The  leather  skin  forms  placoid  scales  or 
small  bony  tablets,  as  in  the  Selachii. 

VII.  Seventh  Period  :  Skin  of  Amphibia. 

The  outer  skin  differentiates  into  an  outer  horn-layer,  and  an  inner 
mucous  layer.  The  ends  of  the  toes  are  covered  with  horny  sheaths  (first 
rudiments  of  claws  or  nails). 

VIII.  Eighth  Period  :  Skin  of  Mammals. 

The  outer  skin  forms  the  appendages  characteristic  of  Mammals  only ; 
hair,  and  sebaceous,  sweat,  and  milk  glands. 


TABLE    XXVIII. 

Systematic  Survey  or  the  most  important  Periods  in  the  Phylogeny 
of  the  Human  Nervous  System. 

I.  First  Period  :  Medulla  of  Gastrceads. 

The  nerve  system  is  not  yet  distinct  from  the  skin,  and,  together  with 
the  latter,  is  represented  by  the  simple  cell-stratum  of  the  exoderm,  or 
primary  skin-layer;  as  it  is  at  the  present  day  in  the  gastrula  of  the 
Amphioxus. 

II.  Second  Period  :  Medulla  of  Primitive  Worms. 

The  central  nerve  system  is  yet,  at  first,  a  part  of  the  skin-sensory  layer, 
and  afterwards  consists  of  a  throat  medulla,  a  simple  nerve-ganglion  lying 
above  the  throat ;  as  it  is  now  in  the  lower  Worms :  the  upper  throat- 
gan«:lion. 


SURVEY   OF   HUMAN    NERVOUS   SYSTEM.  23 1 

III.  Third  Period  :  Medulla  of  Chordoma. 

The  central  nerve  system  consists  of  a  simple  medullary  tube,  an 
elongation  of  the  upper  throat  ganglion,  which  is  separated  from  the  intes- 
tine by  a  notochord  (chorda  dorsalis). 

IV.  Fourth  Period  :  Medulla  of  Acrania. 

The  simple  medullary  tube  differentiates  into  two  parts :  a  head,  and  a 
dorsal  part.  The  head  medulla  resembles  a  small,  pear-shaped,  simple 
swelling  (the  primitive  brain,  or  first  rudiment  of  the  brain)  on  the  anterior 
extremity  of  the  long  cylindrical  spinal  marrow. 

V.  Fifth  Period  :  Medulla  of  Cyclostoma. 

The  simple,  bladder-like  rudiment  of  the  brain  divides  into  five  con- 
secutive brain-bladders  of  simple  structure. 

VI.  Sixth  Period  :  Medulla  of  Primitive  Fishes. 

The  five  brain-bladders  differentiate  into  a  form  similar  to  that  now 
permanently  retained  by  the  Selachii. 

VII.  Seventh  Period  :  Medulla  of  Amphibia. 

The  differentiation  of  the  five  brain-bladders  progresses  to  that  structure 
which  is  now  characteristic  of  the  brain  in  Amphibia. 

VIII.  Eighth  Period  :  Medulla  of  Mammals. 

The  brain  attains  the  characteristic  peculiarities  distinctive  of  Mammals. 
The  following  may  be  distinguished  as  subordinate  stages  of  development ; 
1,  the  brain  of  Monotremes  ;  2,  the  brain  of  Marsupials  ;  3,  the  brain  of 
Semi-apes  ;  4,  the  brain  of  Apes ;  5,  the  brain  of  Man-like  Apes ;  6,  the 
brain  of  Ape-men ;  and  7,  the  brain  of  Man. 


(      232      ) 


TABLE    XXIX. 

Systematic  Survey  of  the  Evolution  of  the  Skin-covering  and 
Nerve  System. 

XXIX.  A.   Survey  of  the  Evolution  of  the  Skin-covering. 


f  /Horn-layer  of  the  outer  /Hair 

Outer-skin  I      skin  I  Nails 

{Epidermis)  J      (Stratum  corneum)       )  Sweat  glands 

Product  of  the  Skin-  \  Mucous    layer    of    the  )  Tear  glands 


Skin 

{Derma, 

or 

InUgumentum) 


sensory-layer 


Leather-skin 
(Corium) 


I      outer  skin  Sebaceous  glands 

\     (Stratum  mucosum)    I  Milk  glands 

.,     /  Connective  tissue 
me    Fatty  tissue 

Muscular  tissue 


/Fibrous  layer 
I  leather  skin 
(Cutis) 


(eunum)  i  i^uks;  J  Blood-vessels 

Product  of  the  Skin-1  Fatty  layer  of  the  leatherl  j^VlU^  of  taste  and 
fibrous-layer  skin  *^ws       of       the 

(Subcutis)  {    leather  skin 


XXIX.  B.   Survey  of  the  Evolution  of  the  Central  Marrow. 


Central  Marrow, 

or 

Central  Nerve 

System 

(Psyche,  or  Medulla 
Centralis). 

Product  of  the 

Skin-sensory 

layer 


(Great  hemispheres 
Olfactory  lobules 
Lateral  chambers 
Streaked  bodies 
Arch 
Cross  piece 

f  Centre  of  sight 

„_.....  I  Third   chamber  of   the 

II.  Twixt-bram  I      brajn 

(Deutopsyche)    ,  pineal  body 
(.Funnel 

in    -.t-j  t    •  r  Four  bulbs 

III.  Mid-brain  I  Aqueduct  of  Sylvius 

(Mesopsyche)     jBl4instalka 

T.r    IT.    .  ,     .  ("Small  hemispheres 

IV.  Hind-brain  J  Brain  worm 

(Metapsyche)     jBrain  bridge 


f  Pyramids 
I  Olives 

■{  Restiform  bodies 
|  Fourth  chamber  of  the 
(_     brain 


V.  After-brain 
{Epipsyche) 


i  VI.  Dorsal  Marrow        Notopsyche 


Eemifphmrai  cerebri 

Lobi  olfactorii 

Vt  n  trie  id  i  laterales 

Corpora  striata 

Fornix 

Corpus  callosum 

Thalami  optici 
Yentrieulus  tertius 

Conarium 
Infundibulum 

Corpus  bigeminum 
Acpurduetus  Sylvii 
1'edunculi  cerebri 

ITcmisphcerce  cerebelli 
Venn  is  cerebelli 
Pons  Varolii 

Corpora  pyramidalia 
Corpora  oliraria 
Corpora  restiformia 
Ventriculus  quartus 


Medulla  spinalis 


Medullary 
coverings 

{Meninges) 


t  Enveloping        mem-  f  j   Soft  medullary  skin       Pia  mater 
Manes,    witfi itne  u .  Central  medullary  skin  Arachnoidal 

4     nutritive         blood- 1  „ 
j      vessels  of  the  brain  I 
{     and  spinal  cord         \ 


Hard  medullary  skin      Dura  mater 
(Products  of  the  skin-fibrous  layer) 


CHAPTER  XXI. 

DEVELOPMENT   OF   THE   SENSE-ORGANS. 

Origin  of  the  most  highly  Purposive  Sense-organs  by  no  Preconceived 
Purpose,  but  simply  by  Natural  Selection. — The  Six  Sense-organs  and 
the  Seven  Sense-functions. — All  the  Sense-organs  originally  Developed 
from  the  Outer  Skin-covering  (from  the  Skin-sensory  Layer). — Organs 
of  the  Pressure  Sense,  the  Heat  Sense,  the  Sexual  Sense,  and  the 
Taste  Sense. — Structure  of  the  Organ  of  Scent. — The  Blind  Nose-pits 
of  Fishes. — The  Nasal  Furrows  change  into  Nasal  Canals.— Separation 
of  the  Cavities  of  the  Nose  and  Mouth  by  the  Palate  Roof. — Structure 
of  the  Eye. — The  Primary  Eye  Vesicles  (Stalked  Protuberances  from 
the  Twixt-brain). — Inversion  of  this  Eye  Vesicle  by  the  Crystalline 
Lens,  separated  from  the  Horn-plate. — Inversion  of  the  Vitreous  Body. 
— The  Vascular  Capsule  and  the  Fibrous  Capsule  of  the  Eyeball. — Eye- 
lids.—  Structure  of  the  Ear. — The  Apparatus  for  Perception  of  Sound  : 
Labyrinth  and  Auditor}'  Nerve. — Origin  of  the  Labyrinth  from  the 
Primitive  Ear  Vesicles  (by  Separation  from  the  Horn-plate). —  Conduct- 
ing Apparatus  of  Sound  :  Drum  Cavity,  Ear  Bonelets,  and  Drum  Mem- 
brane.— Origin  of  these  from  the  First  Gill-opening  and  the  Parts 
immediately  round  it  (the  First  and  Second  Gill-arch). — Rudimentary 
Outer  Ear. — Rudimentary  Muscles  of  the  Ear-shell. 

"  Systematic  Physiology  is  based  especially  upon  the  history  of  develop- 
ment, and  unless  this  is  more  complete,  can  never  make  rapid  progress ;  for 
the  liistory  of  development  furnishes  the  philosopher  with  the  materials 
necessary  for  the  secure  construction  of  a  system  of  organic  life.  Hence 
anatomical  and  physiological  researches  should  be  prosecuted  more  from  tho 


234  THE   EVOLUTION   OF   MAN. 

point  of  view  of  development  than  is  now  the  case  ;  that  is,  we  should  study 
each  organ,  each  tissue,  and  even  each  function  simply  with  the  view  of 
determining  whence  they  have  arisen." — Emil  Huschke  (1832). 


The  sense-organs  are  undeniably  among  the  most  important 
and  most  interesting  parts  of  the  human  body ;  through 
their  activity  alone  we  recognize  the  objects  in  the  world 
around  us.  "  Nihil  est  in  intellectu,  quod  non  prius  fuerit  in 
sensu."  They  are  the  true  springs  of  our  mental  life.  In  no 
other  part  of  the  animal  body  can  we  point  to  such  extremely 
delicate  and  complex  anatomical  contrivances,  co-operating 
for  a  definite  physiological  aim ;  and  in  no  other  part  of  the 
body  do  these  wonderful  and  very  apt  contrivances  seem,  at 
first,  to  indicate  a  premeditated  creative  design  so  conclu- 
sively. Hence  it  is  that,  in  accordance  with  the  received 
teleological  view,  it  has  been  customary  to  admire  the  so- 
called  "  wisdom  of  the  Creator  "  and  the  "  purposive  con- 
trivances of  His  Creation  "  especially  in  this  matter.  But 
on  more  mature  consideration  it  will  be  observed  that  the 
Creator,  according  to  this  conception,  does  after  all  but  play 
the  part  of  an  ingenious  mechanic  or  of  a  skilful  watch- 
maker ;  just,  indeed,  as  all  these  cherished  teleological 
conceptions  of  the  Creator  and  His  Creation  are  based  on 
childish  anthropomorphism. 

We  admit  that  at  first  sight  this  teleological  explana- 
tion seems  to  afford  the  simplest  and  fittest  interpretation 
of  these  very  apt  contrivances.  If  the  structure  and  func- 
tions of  the  very  highly  developed  sense-organs  are  alone 
regarded,  it  seems  as  though  their  origin  is  hardly  explic- 
able except  on  the  assumption  of  a  supernatural  creative 
act.     But  it  is  exactly  on  this  point  that  the  history   of 


ORGANS   OF   SENSE.  235 

evolution  proves  most  clearly  that  this  received  conception 
is  radically  false.  The  history  of  evolution  convinces  us  that 
the  highly  purposive  and  admirably  constituted  sense  organs, 
like  all  other  organs,  have  developed  without  premeditated 
aim ;  that  they  originated  by  the  same  mechanical  process 
of  Natural  Selection,  by  the  same  constant  interaction 
of  Adaptation  and  Heredity,  by  which  all  the  other  pur- 
posive contrivances  of  the  animal  organization  have  been 
slowly  and  gradually  evolved  during  the  "  Struggle  for 
Existence." 

Like  most  other  Vertebrates,  Man  possesses  six  distinct 
organs  of  sense,  which  accomplish  seven  distinct  sensations. 
The  external  skin-covering  accomplishes  the  sensation  of 
pressure  (resistance)  and  of  temperature  (warmth  and  cold). 
This  is  the  earliest,  the  lowest,  and  the  least  differentiated 
organ  of  sense ;  it  is  distributed  over  the  entire  surface  of 
the  body.  The  other  sensorial  activities  are  localized.  The 
sexual  sense  is  limited  to  the  skin-covering  of  the  external 
sexual  organs,  just  as  the  sense  of  taste  is  limited  to  the 
mucous  membrane  of  the  mouth-cavity  (tongue  and  palate), 
and  the  sense  of  smell  to  the  mucous  membrane  of  the 
nose-cavity.  Special  mechanical  contrivances  of  great  com- 
plexity exist  for  the  two  highest  and  most  differentiated 
organs  of  sense,  the  eye  for  the  sense  of  sight,  and  the  ear 
fur  that  of  hearing. 

Comparative  Anatomy  and  Physiology  show  that  in  the 
low  animals  specialized  sense-organs  are  entirely  wanting,  and 
that  all  sensations  are  transmitted  through  the  outer  surface 
of  the  skin-covering.  The  undifferentiated  skin-layer,  or  exo- 
derm,  of  thu  Gastnea  is  the  simple  cell-layer  from  which  the 


236  THE   EVOLUTION   OF  MAN. 

differentiated  sense-organs  of  all  Intestinal  Animals  {Metazoa), 
and,  therefore,  of  all  Vertebrates,  originally  developed.  Start- 
ing from  the  consideration  that  necessarily  only  the  most 
superficial  parts  of  the  body,  those  immediately  exposed  to 
the  outer  world,  could  have  accomplished  sensations,  we 
should  be  justified  in  conjecturing  a  priori  that  the  organs  of 
sense  also  owe  their  origin  to  the  same  part.  This  is,  indeed, 
the  fact.  The  most  important  part  of  all  sense-organs 
develops  from  the  outermost  germ-layer,  from  the  skin- 
sensory  layer ;  in  part,  directly  from  the  horn-plate,  and,  in 
part,  from  the  brain,  the  foremost  section  of  the  medullary 
tube,  after  this  has  separated  from  the  horn-plate.  On 
comparing  the  individual  development  of  the  various  organs 
of  sense,  we  see  that  at  first  they  make  their  appearance  in 
the  simplest  conceivable  form  :  only  very  gradually  does 
that  wonderful  perfect  structure  develop  by  which  the 
higher  sense-organs  eventually  become  the  most  remarkable 
and  the  most  complex  mechanisms  of  the  entire  organiza- 
tion. All  organs  of  sense  are,  however,  originally  merely 
portions  of  the  external  skin-covering,  in  which  sensorial 
nerves  are  distributed.  Even  these  nerves  were  originally 
homogeneous  and  undifferentiated  in  character.  Gradually, 
by  division  of  labour,  the  various  functions  or  "  specific 
energies"  of  the  different  sensorial  nerves  developed.  Simul- 
taneously the  simple  terminal  expansions  of  these  sense 
nerves  in  the  skin-covering  developed  into  extremely  com- 
plex organs. 

The  important  bearings  of  these  historic  facts  upon  the 
just  appreciation  of  mental  life  will  readily  be  perceived. 
The  whole  philosophy  of  the  future  will  assume  another 


NATURAL   SYSTEM   OF   PSYCHOLOGY.  237 

form  as  soon  as  Ps}rchology  has  gained  an  accurate  know- 
ledge of  these  genetic  facts,  and  has  made  them  the  basis  of 
its  speculations. 

If  the  psychological  teachings,  published  by  the  best- 
known  speculative  philosophers,  and  still  generally  received, 
are  impartially  studied,  the  simplicity  with  which  the  authors 
bring  forward  their  airy  metaphysical  speculations,  regardless 
of  all  the  significant  ontogenetic  facts  by  which  their 
doctrines  are  clearly  refuted,  cannot  fail  to  cause  great  sur- 
prise. And  yet  the  history  of  evolution,  in  conjunction 
with  the  rapidly  advancing  Comparative  Anatomy  and 
Physiology  of  the  sense-organs,  affords  the  only  safe  founda- 
tion for  the  natural  theory  of  the  mind. 

With  reference  to  the  terminal  expansions  of  the 
sensory  nerves,  the  human  organs  of  sense  may  be  distri- 
buted into  three  groups,  corresponding  to  three  different 
stages  of  development.  The  first  group  includes  those 
sense-organs,  the  nerves  of  which  distribute  themselves 
simply  in  the  free  surface  of  the  skin-covering  (organs  of 
the  sense  of  pressure,  of  heat,  and  of  the  sexual  sense).  In 
the  second  group,  the  nerves  distribute  themselves  in  the 
mucous  membrane  of  cavities,  which  are  originally  grooves 
or  inversions  of  the  skin-covering  (organs  of  taste  and  of 
smell).  Finally,  the  third  group  is  constituted  by  those 
very  highly  developed  sense-organs,  the  nerves  of  which 
distribute  themselves  over  an  internal  vesicle  detached  from 
the  skin-covering  (organs  of  sight  and  hearing).  This 
remarkable  genetic  relation  is  represented  in  the  following 
table : — 


238 


THE   EVOLUTION   OF   MAN. 


Three  Groups. 


Sense-organs. 


Sense-nerrcs. 


Sense-functions. 


f  I.  Skin-coverim 


A.  Sense-organs  in 
which  the  ter- 
minal expansions 
of  the  nerves  are<< 
distributed  in  the 
outer  skin-cover. 
ing. 


(outer  skin,  or 
epidermis,  and 
leather  -  skin, 
or  coriuni) 
II.  External 
sexual  parts 
(pents  and  cli- 
toris) 


B.  Sense-organs  in  I" III.  Mucous mem- 


which  the  ter- 
minal expansions 
of  the  nerves  are 
distributed  over 
inverted  grooves 
of  the  outer  skin- 


brane  of  the 
mouth  -  cavity 
(tongue  and 
palate) 
IV.  Mucous  mem- 
brane of  the 
nose-cavity 


C.  Sense-organs  in  f 
which     the    ter-  | 
rninal  expansions  I    y    g„e 
of  the  nerves  are 


distribui  e  1   over-' 

vesicles  sepa- 
rated from  the 
external  skin- 
covering. 


VI.  Ear 


I.  Skin  nerves     ■  Sense  of  pressure 
(nervi  cutcmei)  I  Sense  of  warmth 


II.  Sexual  nerves    3.  Sexual  sense 
(nervi  pudendi) 


III.  Taste  nerve      4.  Sense  of  taste 
(nervus  glosso- 
pharyngeus) 


IV.  Olfactory  5.  Sense  of  smell 

nerve 
(n.  olfactorius) 


V.  Sight  nerve  6.  Sense  of  sight 
(n.  opticus) 

VI.  Ear-nerve  7.  Sense  of  hear- 
(».  acousticus)  ing 


Of  the  developmental  history  of  the  lower  organs  of 
sense  I  have  but  little  to  say.  The  development  of  the  skin- 
covering,  which  is  the  organ  of  the  sense  of  pressure  (sense 
of  touch)  and  of  warmth,  wre  have  already  traced  (p.  209). 
I  need  only  add  that  in  the  leather  skin  (corium)  of  Man, 
as  of  all  higher  Vertebrates,  innumerable  microscopic  sense- 
organs  develop,  the  direct  relations  of  which  to  the  sensa- 
tions of  pressure  or  resistance,  of  warmth  and  of  cold,  are 
not  yet  ascertained.  These  organs,  in  or  upon  Avhich  the 
sensitive  skin-nerves  terminate,  are  the  so-called  "  touch 
bodies  "  and  the  "  Pacinian  bodies,"  named  after  their  dis- 


MUCOUS   MEMBRANE   OF   THE   TONGUE   AND   NOSE.      239 

coverer,  Pacini.  Similar  bodies  are  also  found  in  the  organs 
of  the  sexual  sense,  in  the  penis  of  the  male  and  in  the 
clitoris  of  the  female ;  these  are  processes  of  the  integument, 
and  the  development  of  which  we  shall  consider  presently, 
in  connection  with  that  of  the  other  organs  of  generation. 
The  development  of  the  organ  of  taste,  the  tongue  and  the 
palate,  we  will  also  consider  presently,  in  connection  with 
that  of  the  intestinal  canal,  to  which  these  parts  belong. 
To  one  point,  however,  I  will  now  call  particular  attention, 
viz.,  the  mucous  membrane  of  the  tongue  and  palate,  in 
which  the  taste-nerve  terminates,  is  also  in  its  origin  a  portion 
of  the  external  skin-covering.  For,  as  we  found,  the  entire 
mouth-cavity  originates,  not  as  a  part  of  the  actual  intes- 
tinal canal,  but  as  a  groove-like  inversion  of  the  external 
skin  (vol.  i.  p.  338).  Its  mucous  membrane,  therefore,  is 
formed,  not  from  the  intestinal  layer,  but  from  the  skin- 
layer,  and  the  taste-cells  on  the  upper  surface  of  the  tongue 
and  palate  arise,  not  from  the  intestinal-glandular  layer, 
but  from  the  skin-sensory  layer. 

This  is  equally  true  of  the  mucous  membrane  of  the 
organ  of  smell,  the  nose.  The  history  of  the  development 
of  this  sense-organ  is,  however,  of  far  higher  interest. 
Although  the  human  nose,  externally  viewed,  seems  simple 
and  single,  yet  in  Man,  as  in  all  higher  Vertebrates,  it 
consists  of  two  perfectly  distinct  halves,  of  a  right  and  a  left 
nasal  cavity.  These  two  cavities  are  entirely  separated  by 
a  vertical  partition,  so  that  the  passage  into  the  right  nasal 
cavity  lies  only  through  the  right  nostril,  and  into  the  left 
cavity  only  through  the  left  nostril.  Posteriorly  the  two 
nasal  cavities  open  separately  through  the  two  posterior 
nasal  apertures  into  the  head  of  the  pharynx,  so  that  the 


24O  THE    EVOLUTION   OF   MAN. 

pharynx  may  be  entered  without  touching  the  cavity  of  the 
mouth.  This  is  the  passage  by  which  air  is  usually  inhaled; 
the  mouth  being  shut,  it  enters  the  pharynx,  and  thence 
passes  through  the  windpipe  into  the  lungs.  Both  nasal 
cavities  are  separated  from  the  mouth-cavity  by  the  hori- 
zontal bony  palate  roof,  to  the  back  of  which  the  soft 
palate  and  the  uvula  is  attached,  like  a  hanging  curtain. 
In  the  upper  and  hinder  portion  of  both  nasal  cavities  the 
olfactory  nerve  extends  over  the  mucous  membrane,  which 
lines  these  parts.  This  is  the  first  pair  of  brain  nerves, 
which  issue  from  the  skull-cavity  through  the  sieve  bone. 
Its  branches  extend  partly  over  the  partition  wall,  and 
partly  over  the  inner  side-walls  of  the  nasal  cavities,  to 
which  are  attached  the  "'  shells,"  or  spongy  bones  of  the 
nose — complex  bony  structures.  These  "  shells  "  are  much 
further  developed  in  many  of  the  higher  Mammals  than 
in  Man.  In  all  Mammals  there  are  three  of  these  "  shells  " 
in  each  of  the  two  nasal  cavities.  The  sensation  of  smell 
is  produced  by  a  current  of  air,  containing  odorifei'ous 
matters,  passing  over  the  mucous  membrane  of  the  cavities, 
and  there  corning  in  contact  with  nerve-ends. 

The  peculiar  characters  which  distinguish  the  olfactory 
organ  of  Mammals  from  that  of  lower  Vertebrates,  are 
represented  in  Man.  In  all  specific  points  the  human  nose 
exactly  resembles  that  of  the  Catarhine  Apes,  some  of  which 
indeed  possess  an  entirely  human  external  nose  (see  face 
of  the  Nose-ape,  Fig.  202,  p.  175).  The  first  rudiment  of  the 
olfactory  organ  in  the  human  embryo  does  not,  however, 
show  any  signs  of  the  fine  form  of  the  future  catarhine 
nose.  Indeed,  it  first  appears  in  the  same  form  which 
persists  for  life  in  Fishes ;  in  the  form  of  two  simple  pits, 


THE   NOSE.  24I 

or  grooves  in  the  skin  of  the  upper  surface  of  the  head.  In 
all  Fishes  two  of  these  mere  blind  nose-pits  are  found  in 
the  upper  surface  of  the  head  ;  sometimes  they  are  situated 
at  the  back,  near  the  eyes,  sometimes  near  the  snout,  or, 
again,  near  the  mouth-opening  (Fig.  191,  n,  p.  113).  They  are 
lined  by  mucous  membrane  in  folds,  over  which  the  end 
branches  of  the  olfactory  nerves  spread. 

In  this  its  original  condition  the  double  nose  of  all 
Amphirhina  (p.  101)  is  entirely  unconnected  with  the  pri- 
mitive mouth-cavity.     The  connection,  however,  begins  to 


Fig.  231.— Head  of  a  Shark  (Scyl- 
lium),  from  the  ventral  side  :  m,  mouth 
opening ;  o,  nose  grooves,  or  pits ;  r, 
nasal  furrow ;  r?,  nose-flap  in  its 
natural  position ;  n',  nose-flap  turned 
up.  (The  dots  are  openings  of  mucous 
ducts.)     (After  Gegenbaur.) 


appear  even  in  some  Primitive  Fishes  (Selachii) ;  a  super- 
ficial skin-furrow  extends  on  each  side  from  the  nose-groove 
down  to  the  adjacent  corner  of  the  mouth.  This  furrow, 
the  nasal  channel,  or  furrow  (Fig.  231,  r),  is  of  great  sig- 
nificance. In  many  Sharks  (e.g.,  Scyllium)  a  special  process 
of  the  frontal  skin,  the  nasal  flap,  or  "  inner  nasal  process," 
overlaps  the  nasal  furrow  (n,  n').  Opposite  to  this  the  outer 
edge  of  the  furrow  rises  and  forms  the  "outer  nasal  process." 
In  Dipneusta  and  Amphibia  these  two  nasal  processes  meet 
over  the  furrow  and  coalesce,  thus  forming  a  canal,  the 
"  nasal  canal."  There  is  now  a  passage  from  the  external 
nasal  groove  through  this  canal  directly  into  the  mouth- 


242  THE   EVOLUTION   OF  MAN. 

cavity,  which  latter  was  developed  independently  of  the 
groove.  In  the  Dipneusta  and  the  lower  Amphibia  the 
internal  opening  of  the  nasal  canal  lies  well  forward  (behind 
the  lips) ;  in  the  higher  Amphibia  it  lies  further  back.  In 
the  three  highest  vertebrate  classes,  the  Amniota,  the 
primary  mouth-cavity  is  separated  by  the  formation  of  the 
horizontal  palate  roof  into  two  perfectly  distinct  cavities, 
the  superior  (or  secondary)  nasal  cavity,  and  the  inferior 
(or  secondary)  mouth-cavity.  The  nasal  cavity  is  also 
separated  by  the  vertical  partition  into  two  distinct  halves, 
into  a  right  and  a  left  nasal  cavity. 

Comparative  Anatomy  thus  still  shows  us  simultaneously, 
in  the  ascending  series  of  the  double-nostrilled  Vertebrates, 
from  Fishes  up  to  Man,  all  the  various  stages  of  develop- 
ment of  the  nose  which  the  very  highly  developed  olfactory 
organ  of  the  higher  Mammals  has  passed  through  succes- 
sively in  the  different  periods  of  its  tribal  history.  The 
first  rudiment  of  the  organ  of  smell  in  the  embryo  of  Man 
and  in  that  of  all  the  higher  Mammals,  makes  its  appearance 
in  the  same  entirely  simple  form  which  is  retained  throughout 
life  by  the  nose  of  Fishes.  At  a  very  early  stage,  and 
while  no  ti'ace  of  the  characteristic  facial  structure  of  Man 
is  yet  visible,  a  pair  of  small  grooves  appear  on  the  front 
of  the  head,  and  before  the  primitive  mouth-cavity ;  these 
were  first  discovered  by  Baer,  and  by  him  properly  enough 
named  "  olfactory  grooves  "  ("  Eiechgruben,"  Figs.  232,  n, 
233,  n).  These  primitive  nasal  grooves  are  quite  separate 
from  the  primitive  mouth-cavity,  or  mouth  indentation, 
which,  as  we  found,  likewise  makes  its  appearance  as  a 
groove-like  indentation  of  the  external  skin-covering,  in 
front  of  the  blind  anterior  extremity  of  the  intestinal  canal. 


DEVELOPMENT   OF   THE   NOSE. 


243 


This  pair  of  nasal  grooves,  as  well  as  the    single  mouth 
groove    (Fig.   235,  m),   is  lined   by   the  horn-plate.      The 


Fig.  232. 


Fig.  233. 


Fig.  235. 


Fig.  236. 


Figs.  232,  233. — Head  of  an  embryonic  Chick,  on  the  third  day  of 
incubation  :  232,  from  the  front ;  233,  from  the  right  side,  n,  Nose-rudi- 
ment (olfactory  grooves) ;  I,  eye-rudiment  (sight-grooves) ;  g,  ear-rudiment 
(auditory  grooves) ;  v,  fore-brain ;  gl,  eye-slits ;  o,  upper  jaw  process ;  u, 
lower  jaw  process  of  the  first  gill  arch. 

Fig.  231. — Head  of  an  embryonic  Chick,  on  the  fourth  clay  of  incubation, 
from  below:  «,  nose-groove ;  o,  upper  jaw  process  of  the  first  gill  arch; 
■'.  lower  jaw  process  of  the  same  ;  k",  second  gill-arch ;  sp,  choroidal  fissure 
of  the  eye  ;  s,  throat  (pharynx). 

Figs.  235,  236. — Two  heads  of  embryonic  Chicks  :  235,  at  the  end  of  the 
fourth  day ;  236,  at  the  end  of  the  fifth  day  of  incubation.  The  letters  as  in 
Fig.  231.  Additional  letters  are  in,  inner,  and  an,  outer  nasal  process;  nf, 
nasal  furrow  ;  st,  frontal  process  ;  m,  mouth-cavity.     (After  Koelliker.) 

All  these  figures  arc  proportionately  enlarged. 


244  THE   EVOLUTION   OF   MAN. 

original  separation  of  the  nasal  groove  from  the  mouth 
groove  is,  however,  soon  interrupted,  for  the  frontal  process 
(Fig.  235,  st,  Rathke's  "  Nasenfortsatz  der  Stirnwand") 
is  immediately  formed  above  the  mouth  groove.  Right  and 
left  the  edges  of  this  process  project  in  the  form  of  two 
lateral  processes  :  these  are  the  inner  nasal  processes,  or 
nasal  flaps  (Fig.  235,  in).  On  each  side,  opposite  to  these 
rises  a  parallel  ridge  between  the  eye  and  the  nasal  groove. 
These  ridges  are  the  outer  nasal  processes  (Rathke's  "Nasen- 
dacher,"  Fig.  235,  an).  Between  the  inner  and  outer 
nasal  process  a  channel-like  depression  thus  extends  on 
each  side  from  the  nose  groove  toward  the  mouth  groove 
(m),  and  this  channel  is,  of  course,  the  same  nasal  furrow 
or  channel  which  we  found  in  the  Shark  (Fig.  231,  r).  As 
the  two  parallel  edges  of  the  inner  and  the  outer  nasal 
processes  bend  towards  each  other  and  coalesce  above  the 
nasal  channel,  the  latter  becomes  a  small  tube — the  primitive 
"  nasal  canal."  In  this  stage  of  its  Ontogeny,  therefore,  the 
nose  of  Man  and  of  all  other  Amnion  Animals  consists  of 
two  small  narrow  tubes — the  "  nasal  canals  " — leading  from 
the  outer  surface  of  the  frontal  skin  into  the  simple  pri- 
mitive mouth-cavity.  This  transient  condition  resembles 
the  permanent  condition  of  the  nose  in  Dipneusta  and 
Amphibia.     (Cf.  Plate  I.,  Frontispiece,  with  explanation.) 

Specially  significant  in  the  modification  of  the  open  nasal 
channel  into  the  closed  nasal  canal,  is  a  plug-shaped  forma- 
tion, which  extends  from  below  up  to  the  lower  extremities 
of  both  the  nasal  processes  on  each  side,  and  unites  with 
them.  This  is  the  upper  jaw  process  (Figs.  232,  o,  236,  o, 
Plate  I.,  o).  Below  the  mouth  groove  lie  the  gill  arches, 
which  are  separated  from  one  another  by  the  gill  openings 


UPPER   JAW   PROCESS.  245 

(Plates  I.,  VI.,  and  VII.,  k).  The  first  of  these  gill  arches,  at 
present  the  most  interesting  to  us,  which  we  may  call  the 
jaw  arch,  develops  the  jaw-skeleton  of  the  mouth  (Plate  I.,  u). 
A  small  process  first  grows  out  from  the  base  of  the  front 
gill-arch :  this  is  the  upper  jaw  process.  The  first  gill-arch 
itself  develops  a  cartilage  on  its  inner  side,  called  after  its 
discoverer,  "Meckel's  cartilage,"  on  the  outer  surface  of 
which  the  lower  jaw  forms  (Figs.  232,  u,  236,  u).  The  upper 
jaw  process  forms  the  principal  part  of  the  entire  framework 
of  the  upper  jaw,  viz.,  the  palate  bone  and  the  wing  bone. 
On  its  outer  side  the  upper  jaw  bone,  in  the  narrower  sense, 
afterwards  arises,  while  the  middle  portion  of  the  upper  jaw 
skeleton,  the  twixt  jaw  (intermaxillary  bone)  develops 
from  the  anterior  portion  of  the  frontal  process.  (See 
development  of  the  face  in  Plate  I.) 

In  the  further  characteristic  development  of  the  face  in 
the  three  higher  vertebrate  classes,  the  two  upper  jaw  pro- 
cesses are  of  the  highest  importance.  From  them  proceeds 
the  palate  roof,  the  important  horizontal  partition  which 
grows  into  the  simple  primitive  mouth-cavity,  separating 
it  into  two  quite  distinct  cavities.  The  upper  cavity, 
into  which  the  two  nasal  cavities  open,  now  develops  into 
the  nasal  cavity — a  respiratory  air  passage  and  an  olfactory 
organ.  The  lower  cavity,  on  the  other  hand,  forms,  by  itself, 
the  permanent  secondary  mouth-cavity  (Fig.  237,  ni) — the 
digestive  food  passage  and  the  organ  of  taste.  Both  the  upper 
smell-cavity  and  the  lower  taste-cavity  open  at  the  back  into 
the  throat  (pharynx).  The  palate  roof,  separating  these  two 
cavities,  is  formed  by  the  coalescence  of  two  lateral  portions 
— of  the  horizontal  plates  of  the  two  upper  jaw  processes 
(palate-plates ;  Fig.  237,  p).     When  these  do  not  perfectly 


246  THE   EVOLUTION   OF  MAN. 

adhere  in  the  middle  line,  the  result  is  a  permanent  longi- 
tudinal cleft,  through  which  there  is  an  open  passage  from 
the  inouth-cavit}^  directly  into  the  nasal  cavity.     The  so- 


Fig.  237.  —  Diagrammatic  transverse  section 
through  the  mouth  and  nose  cavity.  While  the 
palate-plates  (p)  separate  the  original  mouth-cavity 
into  the  lower  secondary  mouth. cavity  (m)  and  the 
npper  nasal  cavity,  the  latter  is  parted  by  the  ver- 
tical partition  wall  of  the  nose  (e)  into  two  distinct 
halves  (n,  11).     (After  Gegenbaur.) 


called  "  wolf's  jaws  "  are  thus  caused.  The  "  hare-lip  "  and 
"  split  lip "  is  a  slighter  degree  of  this  arrested  develop- 
ment.116 

Simultaneously  with  the  horizontal  partition  of  the 
palate  roof,  a  vertical  wall  by  which  the  single  nasal  cavity 
is  divided  into  two,  a  right  and  a  left  cavity,  develops 
(Fig.  237,  n,  n).  This  vertical  partition  of  the  nose  (e)  is 
formed  by  the  middle  part  of  the  frontal  process :  above 
this  gives  rise  by  ossification  to  the  vertical  lamella  of  the 
sieve  bone  (cubiform  plate),  and  below  the  great  vertical 
bony  partition  wall — the  "  plough-share  "  {vomer),  and  in 
front  to  the  twixt-jaw  (os  intermaxillare).  Goethe  was 
the  first  to  show  that  in  Man,  just  as  in  all  the  other  Skulled 
Animals,  the  twixt-jaw  appears  as  an  independent  bone 
between  the  two  halves  of  the  upper  jaw.  The  vertical 
partition  wall  of  the  nose  finally  coalesces  with  the  horizontal 
palate  roof.  The  two  nasal  cavities  are  now  as  entirely 
separate  from  one  another  as  from  the  secondary  mouth- 
cavity.  These  three  cavities  open,  however,  at  the  back 
into  the  pharnyx,  or  jaw-cavity. 


THE   HUMAN    NOSE. 


247 


The  double-nostrilled  nose  has  now  attained  the  structure 
characteristic  of  Man  in  common  with  all  other  Mammals. 
Its  further  development  is  very  easily  intelligible :  it  is 
limited  to  the  formation  of  internal  and  external  processes 
of  the  walls  of  both  nasal  cavities.  Within  the  cavities 
develop  the  "  nose  shells,"  spongy  bony  structures,  over  which 
the  olfactory  mucous  membrane  spreads.  The  first  brain 
nerve,  the  olfactory  nerve,  with  its  delicate  branches,  passes 


Figs.  238,  239. — Upper  part  of  the  body  of  a  human  embryo  (16  mm.  in 
length)  during  the  sixth  week  :  Fig.  238,  from  the  left  side  ;  Fig.  239,  from 
the  front.  The  origin  of  the  nose  in  two  lnteral  halves, 
originally  separate,  is  still  plainly  visible.  The  nose  and 
upper  lip  are  disproportionately  great  in  comparison  with 
the  rest  of  the  face,  especially  with  the  lower  lip. 
(After  Kollman.) 

Fig.  210. — Face  of  a  human  embryo  of  eight  weeks. 
(After  Eoker.)  Cf.  Frontispiece,  Plate  I.  Fig.  Mi— 
Mm. 


■ 


248  THE   EVOLUTION   OF   MAN. 

from  the  large  brain  through  the  roof  of  both  nasal  cavities 
into  the  cavities,  and  extends  over  the  olfactory  mucous 
membrane.  At  the  same  time,  by  inversion  of  the  nasal 
mucous  membrane,  the  minor  cavities  of  the  nose,  which  are 
afterwards  filled  with  air,  and  which  communicate  directly 
with  the  two  nasal  cavities,  arise  (frontal  cavities,  cavities  of 
the  sphenoid  bone,  jaw  cavities,  etc.).  In  this  special  stage 
of  development  they  occur  only  in  Mammals.171 

The  external  nose  is  not  developed  until  long  after  all 
these  essential  internal  parts  of  the  olfactory  organ  have 
been  formed.  The  first  trace  in  the  human  embryo  appears 
at  the  end  of  the  second  month  (Figs.  238-240).  Any 
human  embryo  during  the  first  month  shows  that  originally 
there  is  no  trace  of  the  external  nose.  It  afterwards  grows 
out  from  the  anterior  nasal  portion  of  the  primitive  skull. 
The  form  of  nose  which  is  characteristic  of  Man  does  not 
appear  till  a  period  far  later.  Much  stress  is  usually 
laid  on  the  shape  of  the  external  nose  as  a  noble  organ, 
occurring  exclusively  in  Man ;  but  there  are  Apes  which 
have  very  human  noses,  as,  for  instance,  the  Nosed  Ape 
already  mentioned.  On  the  other  hand,  the  external  nose, 
the  fine  shape  of  which  is  so  extremely  important  to  the 
beauty  of  the  facial  structure,  possesses  in  certain  inferior 
races  of  Man  a  shape  anything  but  beautiful.  In  most 
Apes  the  external  structure  of  the  nose  remains  undeveloped. 
Especially  remarkable  is  the  important  fact  already  cited 
that  it  is  only  in  the  Apes  of  the  Old  World,  in  the  Cata- 
rhines,  that  the  nasal  partition  wall  (sejptum)  remains  as 
small  as  it  is  in  Man ;  in  Apes  of  the  New  World  it  widens 
considerably  at  the  base,  so  that  the  nostrils  open  outwards 
(Platyrhini,  p.  175). 


(     249     ) 

TABLE    XXX. 

Systematic  Survey  of  the  Chief  Phylogenetic  Stages  of  the 
Human  Nose. 

First  Stage  :  Nose  of  the  earlier  Primitive  Fishes. 

The  nose  is  formed  by  a  pair  of  simple  skin-grooves  (nose-pits)  in  the 
outer  surface  of  the  head  (like  those  which  are  now  permanently  retained 
by  the  lower  Selachians). 

Second  Stage  :  Nose  of  the  more  recent  Primitive  Fishes. 
Each  of  the   two  blind  nasal  grooves  becomes  connected  by  a  furrow 
(nasal-furrow)  with  one  end  of  the  mouth  (as  is  yet  permanently  the  case  in 
the  higher  Selachians). 

Third  Stage  :  Nose  of  the  Dipneusta. 

The  two  nasal  furrows  change,  in  consequence  of  the  coalescence  of  their 
edges,  into  closed  canals  (primary  nose-canals),  which  open  at  their  front 
ends,  within  the  soft  edges  of  the  lip,  into  the  primary  mouth-cavity;  as  is 
yet  permanently  the  case  in  the  Dipneusta  and  the  earlier  lower  Amphibia 
(Sozobranchia). 

Fourth  Stage:  Nose  of  Amphibia. 
The  inner  openings  of  the  nasal  canals  penetrate  further  back  into  the 
primary  mouth-cavity,  so  that  they  are  surrounded  by  hard  bony  portions  of 
the  jaw  (as  is  yet  permanently  the  case  in  the  higher  Amphibia). 

Fifth  Stage  :  Nose  of  the  Protamnia, 

The  primitive  mouth-cavity,  into  which  both  nasal  canals  open,  separates, 
in  consequence  of  the  formation  of  a  horizontal  partition  (the  palate-roof), 
into  an  upper  nasal  cavity  and  a  lower  (secondary)  mouth-cavity.  The 
formation  of  the  spongy  bones  of  the  nose  commences  (as  in  the  earlier 
Amnion  Animals). 

Sixth  Stage :  Nose  of  the  earlier  Mammals. 

The  simple  nose-cavity  separates,  in  consequence  of  the  development  of 
a  vertical  partition  wall  (the  "plough,"  vomer),  into  two  distinct  nose-cavities, 
each  of  which  is  occupied  by  one  of  the  nasal  canals  (as  is  yet  the  case  in  all 
Mammals).     The  spongy  nose-bones  differentiate. 

Seventh  Stage  :  Nose  of  the  more  recent  Mammals. 

Within  both  nose-cavities  the  development  of  the  spongy  bones  proceeds 
further,  and  an  external  nose  begins  to  form. 

Eighth  Stage  :  Nose  of  tlie  Catarhine  Apes. 
The   internal   and    the   external    nose    attain   the  full  development  ex- 
clusively characteristic  of  Catarhine  Apes  and  of  Man. 


2$0 


THE   EVOLUTION   OF  MAN. 


The  history  of  the  development  of  the  eye  is  equally 
remarkable  and  instructive.  For  although  the  eye,  owing 
to  its  exquisite  optical  arrangement  and  wonderful  struc- 
ture, is  one  of  the  most  complex  and  most  nicely  adapted 
organs,  yet  it  develops,  without  a  preconceived  design,  from 
a  very  simple  rudiment  in  the  outer  skin-covering. 


Fig.  241. — The  human  eye  in  transverse  section:  a,  protective  membrane 
{sclerotica);  b,  horn  membrane  (cornea);  c,  outer  membrane  (conjunctiva) ; 
d,  circular  veins  of  iris ;  e,  vascular  membrane  (choroidea) ;  f,  ciliary 
muscle ;  g,  corona  ciliaris ;  h,  rainbow  membrane  (iris) ;  i,  optic  nerve 
(n.  opticus);  k,  anterior  limit  of  the  retina;  I,  crystalline  lens  (lens  crystal- 
Una)  ;  m,  inner  cover  of  the  horn  membrane  (water  membrane,  membrana 
Descemeti);  n,  pigment  membrane  (pigmentosa);  o,  retina;  p,  "petits-c&nsd;" 
q,  yellow  spot  of  the  retina.     (After  Helmholtz.) 


When   fully  developed,  the   human   eye  is  a  globular 
capsule  (the  eyeball,  bulbus,  Fig.  241).      This  lies  in  the 


THE   EYE.  251 

bony  orbit  of  the  skull,  surrounded  by  protective  fat  and 
by  motor   muscles.      The  greater  part  of  this   eyeball  is 
occupied  by  a   semi-fluid,   clear  gelatinous  substance,  the 
vitreous    body    {corpus    vitreum).      The    crystalline    lens 
(Fig.  241,  I)  is   embedded  in  the  anterior  surface  of  the 
vitreous  body.     It  is  a  lentil-shaped,  bi-convex,  transparent 
body — the  most  important  of  the  light-refracting  media  of 
the  eye.     Among  these  media  is,  in  addition  to  the  lens 
and  vitreous  body,  the  aqueous  humour  (humor  aqueus,  at 
m,  in  Fig.  241),  in  front  of  the  lens.     These  three  pellucid, 
light-refracting  media — the   vitreous  body,  the  crystalline 
lens,  and  the  aqueous  humour — by  which  the  rays  of  light, 
incident  on  the  eye,  are  refracted   and   concentrated,  are 
enclosed  in  a  firm  globular  capsule  consisting   of  several 
different  membranes,  comparable  with  the  concentric  layers 
of  an  onion.     The  outer  and  thickest  of  these  forms  the 
white  protective  membrane  of  the  eye  (sclerotica,  a).     It 
consists  of  firm,  compact  white  connective  tissue.     In  front 
of  the  lens  a  circular,  very  convex,  transparent  plate,  re- 
sembling a  watch  glass,  is  inserted  in  the  white  protective 
membrane ;    this  is  the  horny  membrane  {cornea,  b).     On 
its  outer  surface  the  horny  membrane  is  covered  by  a  very 
thin   coating   of   outer  skin   (epidermis) ;   this   coating  is 
called  the  connecting  membrane  (conjunctiva);  it  extends 
from  the  horny  membrane  over  the  inner  surface  of  both 
eyelids — the  upper  and  lower  folds  of  skin  which  on  closing 
the   eyes   are   drawn   together    over   them.     At  the  inner 
corner  of  our  eye  there  is,  as  a  sort  of  i-udimentary  organ, 
the  remnant  of  a  third  (inner)  eyelid,  which,  as  the  "  nic- 
titating   membrane,"    is    highly   developed    in    the    lower 
Vertebrates  (vol.  i.  p.  110).    Below  the  upper  eyelid  are  lodged 


252  THE    EVOLUTION    OF    MAN. 

the  tear-glands,  the  secretion  of  which  keeps  the  surface 
of  the  eye  smooth  and  clean. 

Directly  under  the  protective  membrane  is  a  delicate 
dark-red,  highly  vascular  membrane,  the  vascular  mem- 
brane (choroidea,  e),  and  within  this  the  retina  (o),  which 
is  a  dilatation  of  the  optic  nerve  (i).  This  latter  is  the 
second  brain  nerve.  It  extends  from  the  "  centre  of  sight " 
(the  second  brain-bladder)  to  the  eye,  penetrates  the  outer 
coats  of  this,  and  then  extends,  as  the  retina,  between  the 
vascular  membrane  (choroidea)  and  the  vitreous  body 
(corpus  vitreum).  Between  the  retina  and  the  vascular 
membrane  lies  another  very  delicate  membrane,  which 
is  commonly,  but  wrongly,  considered  as  part  of  the  latter. 
This  is  the  black  pigment  membrane  (pigmentosa,  lamina 
pigmenti,  n),  or  the  "  black  carpet "  (tapetum  nigrum). 
It  consists  of  a  single  layer  of  beautiful  hexagonal  cells 
accurately  joined  together  and  filled  with  black  pigment 
granules.  This  pigment  membrane  lines,  not  only  the  inner 
surface  of  the  actual  vascular  membrane,  but  also  the  pos- 
terior surface  of  its  anterior  muscular  prolongation,  which, 
as  a  circular  ring-like  membrane,  covers  the  edge  of  the  lens, 
and  prevents  the  penetration  of  lateral  rays.  This  is  the 
well-known  "rainbow  membrane"  (iris,  h),  which  is  differently 
coloured  in  different  persons  (blue,  gray,  brown,  etc.).  This 
"  rainbow  membrane "  is  the  limit  towards  the  front  of 
the  vascular  membrane.  The  round  hole  in  the  iris  is  the 
pupil,  through  which  the  rays  of  light  pass  into  the  interior 
of  the  eye.  Where  the  iris  proceeds  from  the  edge  of  the 
actual  vascular  membrane,  the  latter  is  much  thickened  and 
forms  a  beautiful  ciliated  crown  (corona  ciliaris,  g),  which 
surrounds  the  edge  of  the  lens  with  about  seventy  large, 
and  many  smaller  rays. 


DEVELOPMENT   OF  THE  EYE. 


253 


In  the  embryo  of  Man,  as  in  that  of  all  other  Amphi- 
rhina,  two  pear-shaped  vesicles  grow  out  laterally,  at  a  very 
early  period,  from  the  foremost  part  of  the  first  brain 
bladder  (Fig.  223,  a,  p.  218).  These  bladder-like  protuberances 
are  the  primary  eye-vesicles.  At  first  they  are  directed 
outward  and  forward,  but  they  soon  make  their  way  further 
downward,  so  that  after  the  specialization  of  the  five  brain- 
bladders,  they  lie  at  the  base  of  the  twixt-brain.  The 
internal  spaces  within  the  two  pear-shaped  vesicles,  which 
soon  attain  a  considerable  size,  communicate  through  their 
hollow  stalks  with  the  cavity  of  the  twixt-brain.  Their 
outer  covering  is  formed  by  the  outer  skin-covering  (horn- 
plate  and  leather-plate).  Where,  on  each  side,  the  latter 
comes  directly  in  contact  with  the  most  curved  portion  of 
the  primary  eye-vesicles,  a  thickening  (I)  arises,  and  at  the 
same  time  a  groove-like  indentation  (0)  in  the  horn-plate 
(Fig.  242, 1).  This  groove,  which  we  will  call  the  lens  groove, 
changes  into  a  closed  sac,  the  thick- walled  lens  vesicle  (2, 1), 
owing:  to  the  fact  that  the  edg-es  of  the  Groove  coalesce  above 


Fig.  24-2. — Eye  of  an  embryonic  Chick  in  longitudinal  section  (1,  of  a 
germ  after  sixty-five  hours  of  incubation;  2,  of  a  somewhat  older  germ; 
3,  of  a  germ  four  days  old) :  h,  horn-plate ;  o,  lens  groove  ;  I,  lens  (in  1, 
it  still  forms  part  of  the  epidermis,  while  in  2  and  3  it  has  separated);  x, 
thickening  of  the  horn-plate  at  the  point  from  which  the  lens  soparated  ; 
gl,  vitreous  body ;  r,  retina;  u,  pigment  membrane.     (After  Remak.) 


254  T1W   EVOLUTION   OF   MAN. 

it.  Exactly  as  the  medullary  tube  originally  separates  from 
the  outer  germ-layer  does  this  lens-sac  separate  from  the 
horn-plate,  in  which  it  originated.  The  space  within  this 
sac  is  afterwards  entirely  filled  by  the  cells  of  its  thick  wall, 
and  the  solid  crystalline  lens  is  thus  formed.  The  latter  is, 
therefore,  purely  a  formation  of  the  epidermis.  Together  with 
the  lens  the  small  fragment  of  the  leather-plate  (corium) 
lying  below  the  lens  separates  from  the  outer  skin-covering. 
This  small  piece  of  the  leather-skin  very  soon  forms  a  highly 
vascular  sac  round  the  lens  (cajisula  vasculosa  lentis). 
Its  anterior  portion  at  first  covers  the  pupillary  orifice,  and 
is  then  known  as  the  pupillary  membrane  (membrana 
papillaris).  Its  back  portion  of  the  same  membrane  is  called 
the  "  membrana  capsulo-pupillaris."  This  "  vascular  lens 
capsule,  which  merely  serves  to  nourish  the  growing  lens," 
afterwards  entirely  disappears.  The  later,  permanent  lens 
capsule  contains  no  vessels,  and  is  a  structureless  secretion 
of  the  lens  cells. 

As  the  lens  thus  separates  from  the  horn-plate  and 
grows  inward,  it  must  necessarily  indent  the  adjoining 
primary  eye-vesicles  from  without  (Fig.  212,  1-3).  This 
process  may  be  compared  to  the  inversion  of  the  germ-mem- 
brane vesicle  (blastula),  which  in  the  Amphioxus  and  in 
many  low  animals  gives  rise  to  the  gastrula  (vol.  i.  p.  192).  In 
both  instances  the  inversion  of  one  side  of  the  closed  vesicle 
proceeds  until  finally  the  inner,  inverted  portion  touches  the 
outer,  uninverted  portion  of  the  wall  of  the  vesicle,  so  that 
the  cavity  disappears.  Just  as  in  the  gastrula  the  former 
part  changes  into  the  intestinal  layer  (entoderma),  and 
the  latter  into  the  skin-layer  (exoderma),  so  in  the  inverted 
primary  eye-vesicle    the   retina  develops  from  the  former 


DEVELOPMENT    OF    THE    EYE.  255 

(inner)  part  (Fig.  242,  r),  and  the  black  pigment  membrane 
(vS)  from  the  latter  (the  outer,  unin verted  part).  The  hollow 
stalk  of  the  primary  eye-vesicle  changes  into  the  optic 
nerve. 

The  lens  (I)  which  enacts  so  important  a  part  in  this 
inverting  process  of  the  primary  eye-vesicle,  lies  at  first 
directly  upon  its  inverted  part,  that  is,  on  the  retina  (r). 
Very  soon,  however,  the  two  separate,  a  new  body,  the 
vitreous  body  {corpus  vitreum,  gl),  coming  in  between  them. 
While  the  lens-sac  is  detaching  itself,  and  the  primary  eye- 
vesicle  is  being  inverted  from  without,  another  inversion 
simultaneously  proceeds  from  beneath — from  the  superficial 
portion  of  the  skin-fibrous  layer,  i.e.,  from  the  leather-plate 
of  the  head.  At  the  back  of  the  lens  and  below  it,  a  ledge-like 
process  of  the  leather-plate  arises  (Fig.  243,  g),  which  inverts 
the  primary  eye-vesicle  (now  shaped  like  a  cup)  from  below, 
and  presses  in  between  the  lens  (I)  and  the  retina  (r) 
Thus  the  primary  eye-vesicle  assumes  the  form  of  a  hood. 
The  opening  of  this  hood,  answering  to  the  face,  is  covered 
by  the  lens ;  but  the  opening,  through  which  the  neck 
would  pass,  answers  to  the  indentation  through  which  the 
leather-skin  passes  in  between  the  lens  and  the  retina  (the 
inner  wall  of  the  hood).  The  space  within  this  secondary 
eye-vesicle  is  almost  filled  by  the  vitreous  body,  which 
answers  to  the  head  wrapped  in  this  hood.  The  hood  itself 
is,  properly  speaking,  double  :  the  inner  hoo'd  itself  is  the 
retina,  and  the  outer  one,  directly  surrounding  the  former, 
is  the  pigment  membrane.  The  comparison  with  a  hood 
renders  this  process  of  inversion,  which  is  sometimes  hard 
to  explain,  more  clearly  understood.  The  rudiment  of  the 
vitreous    body   (corpus    vitreum)   is   at   first   very   incon- 


256  THE   EVOLUTION   OF   MAN. 

siderable  (Fig.  243,  g),  and  the  retina  disproportionally 
thick.  As  the  former  expands,  the  latter  becomes  much 
thinner,  till  at  last  the  retina  appears  only  as  a  very  delicate 

i  h  Fig.  243. — Horizontal  transverse 

_^^^g^L  section  through  the  eye  of  a  human 

••;.«.'  ~'.~,- ,'-.;?  /  embryo   of   four   weeks;    100    times 

enlarged    (after    Koelliker) :    t,   lens 

(the  dark  wall  of  which  is  equal  to 

the  diameter  of  the  central  cavity) ; 

<    ..  -J       g,  vitreous  body  (connected  with  the 

.       ;  •  leather-plate  by  a  stalk,  g')  ;  v,  vas- 

V.  ■    . l  •  '  cular  loop  (penetrating  through  the 

_',  '  stalk  (g')  into  the  vitreous  body  be- 

v^  '  \   ,  hind    the    lens);    r,     retina    (inner, 

v         iy' 

thicker,    inverted     lamella     of     the 

primary   eye-vesicle) ;    a.  pigment   membrane   (outer,  thinner,    uninverted 

lamella  of  the  same) ;  h,  intermediate   space  between  the  retina  and  the 

pigment  membrane  (remnant  of  the  cavity  of  the  primary  eye-vesicle). 

coat  of  the  thick,  almost  globular  vitreous  body,  which  fills 
the  greater  part  of  the  secondary  eye-vesicle.  The  outer 
layer  of  the  vitreous  body  changes  into  a  highly  vascular 
capsule,  the  vessels  of  which  afterwards  disappear. 

The  slit-like  passage  through  which  the  rudiment  of  the 
vitreous  body  grows  from  below  in  between  the  lens  and 
the  retina,  of  course  causes  a  break  in  the  retina  and  the 
pigment-membrane.  This  break,  which  appears  on  the  inner 
surface  of  the  vascular  membrane  as  a  colourless  streak,  has 
been  inaptly  called  the  choroidal  cleft,  though  the  true 
vascular  membrane  is  not  cleft  at  all  at  this  point  (Fig. 
234,  sp,  235,  sp,  p.  243).  A  thin  process  of  the  vitreous  body 
passes  inward  on  the  under  surface  of  the  optic  nerve,  which 
it  inverts  in  the  same  way  as  the  primary  eye-vesicle  was 
inverted.     The  hollow  cylindrical  optic  nerve  (the  stalk  of 


DEVELOPMENT   OF   THE   EYE.  257 

the  primary  eye-vesicle)  is  thus  transformed  into  a  channel, 
opening  downward.  The  inverted  lower  surface  attaches 
itself  to  the  uninverted  upper  surface  of  the  hollow  stalk,  so 
that  the  hollow  space  within  the  stalk,  forming  the  com- 
munication between  the  cavity  of  the  twixt-brain  and  of 
the  primary  eye-vesicle,  now  disappears.  The  two  edges 
of  the  channel  now  grow  downward  toward  each  other, 
enclose  the  band-like  process  of  the  leather-plate,  and 
coalesce  beneath  it.  Thus  this  process  now  lies  within  the 
axis  of  the  solid  secondary  optic  nerve.  It  develops  into 
a  cord  of  connective  tissue  carrying  the  central  blood-vessel 
of  the  retina  (vasa  centralia  retince). 

An  entirely  fibrous  covering,  the  fibrous  capsule  of  the 
eye,  now  finally  forms  round  the  outside  of  the  secondary 
eye-vesicle  and  its  stalk  (the  secondary  optic  nerve).  It 
originates  from  the  head-plate,  from  that  part  of  the  skin- 
fibrous  layer  which  immediately  encloses  the  eye-vesicle. 
This  fibrous  covering  takes  the  form  of  a  completely-closed 
globular  sac,  which  surrounds  the  whole  ball  of  the  eye,  and 
on  the  outer  side  of  this,  grows  in  between  the  lens  and  the 
horn-plate.  The  globular  wall  of  the  capsule  soon  separates, 
by  fission  of  the  surface,  into  two  distinct  membranes.  The 
inner  membrane  becomes  the  choroidea,  or  vascular  layer; 
in  front  it  forms  the  ciliated  crown  {corona  ciliaris)  and 
the  iris.  The  outer  membrane,  on  the  other  hand,  becomes 
the  white  enveloping,  or  protective  membrane  (sclerotica), 
and,  in  front,  forms  the  transparent  horny  membrane 
(cornea).  The  rudiments  of  all  the  essential  parts  of  the 
eye  are  now  formed,  and  its  further  development  is  only  io 
details,  in  the  complex  differentiation  and  combination  of 
the  several  parts. 


(     258    ) 


TABLE    XXXI. 

Systematic  Survey  of  the  Development  of  the  Human  Eye. 


I.  Systematic  Survey  of  those  parts  of  the  Human  Eye  which  develop  from  the  first  of  the 
Secondary  Germ-layers,  the  Skin-sensory  Layer. 


Products  of  the 

Marrow-plate 


Products  of  the 
Horn-plate 


(1.  Stem  of   the   primary      1.  Optic  nerve  Nervus  opticus 

eye-vesicle 

I  2.  Inner  (inverted)  part  of      2.  Retina  Retina 

the    primary    eye- 
vesicle 


|  3.  Outer  (uuin verted) part 
of  the  primary  eye- 
vesicle 


Screen,    or     pig-    Pigmentosa    (lamina 
ment-coat  pigmenti) 


ri.  Vesicle  separated  from      4.  Crystalline  lens         Lens  crystallina 
the  horny  plate 


5.  Outer  epidermic  skin 


3.  Connective  mem-    Conjunctiva 
brane 


6.  Inverted  portions  of  the      6.  Tear-glands 
^        epidermic  skin 


Glandules  lacrymales 


II.  Systematic  Survey  of  those  parts  of  the  Human  Eye  which  develop  from  the  second  of  the 
Secondary  Germ-layers,  the  Skin-fibrous  Layer. 


C. 


f1,S.  Ledge-like  process  of 
the  corium  on  the 
lower  side  of  the  pri- 
mary eye-vesicle 

9.  Continuation    of    the 
corium  process 


Products  of  the    < 

Leather-plate     I  10.  Pupillary     membrane, 
with  its  capsule 


1.  Vitreous  body  Corpus  vitreum 

8.  Vascular      mem-  Capsula  vasculosa 

brane    of    the  corporis  vitrei 
vitreous  body 

9.  Central  vessels  of  Vasa  centralia 

the  retina 


Products  of  the 
Skull-plate 


10.  Vascular  mem- 
brane of  the 
lens 


retina 

Capsula  vasculosa 
lentis  crystalline?. 


11.  Folds  of   the   leather    11.  Eyelids 
skin  (corium) 


Palpebral 


12,  13.  Vascular       mem-  12,  Vascular      mem-     Choroidea 
brane  of    the  eye-  brane 

ball  (capsula  vas-  13.  Rainbow       mem-    Iris 
culosa  bulbi))  brane 

14,  15.  Fibrous  membrane  14.  Protective    mem-    Sclerotica 
of  the  eyeball  (cap-  brane 

sula  fibrosa  bulbi)  15.  Horny  membrane    Cornea 


THE   NICTITATING   MEMBRANE.  259 

The  most  important  fact  in  this  remarkable  process  of 
eye-development  is  the  circumstance  that  the  optic  nerve, 
the  retina,  and  the  pigment-membrane  originate  from  a 
part  of  the  brain,  from  a  protuberance  of  the  twixt-brain, 
while  the  crystalline  lens,  the  most  important  refracting 
medium,  develops  from  the  outer  skin  (epidermis).  From 
the  outer  skin — the  horny  lamina — originates  also  the 
delicate  connecting  membrane  (conjunctiva)  which  after- 
wards envelopes  the  outer  surface  of  the  eyeball.  The  tear- 
glands  proceed,  as  branched  processes,  from  the  conjunctiva 
(Fig.  214,  p.  202).  All  the  other  parts  of  the  eye  originate 
from  the  skin-fibrous  layer;  the  vitreous  body  and  the 
vascular  lens-capsule  from  the  leather-plate,  the  choroid 
coat  with  the  iris,  and  the  protective  membrane  (sclerotica) 
with  the  horny  membrane  (cornea)  from  the  head-plates. 

The  outer  protective  organs  for  the  eye,  the  eyelids,  are 
merely  simple  folds  of  skin,  which,  in  the  human  embryo, 
appear  in  the  third  month.  In  the  fourth  month  the  upper 
eyelid  adheres  to  the  lower,  and  the  eye  then  remains 
covered  by  them  till  birth.  (Plate  VII.  Fig.  M  in.,  R  m., 
etc.)  The  two  eyelids  usually  again  separate  shortly  before 
birth,  but  sometimes  not  till  after.  Our  skulled  ancestors 
had,  in  addition  to  these,  a  third  eyelid,  the  nictitating 
membrane,  which  was  drawn  over  the  eye  from  the  inner 
corner.  Many  Primitive  Fishes  (SelacJiii)  and  Amnion 
Animals  yet  retain  this.  In  Apes  and  in  Man  it  has  atrophied, 
and  only  a  small  remnant  of  it  exists  in  the  inner  corner  of 
the  eye  as  the  "  crescent-shaped  fold,"  as  a  useless  "  rudi- 
mentary organ."  (Cf.  vol.  i.  p.  109.)  Apes  and  Man  have 
also  lost  the  "  Harder  gland,"  opening  below  the  nictitating 
membrane,  which  appears  in  other  Mammals,  and  in  Birds, 
Reptiles,  and  Amphibians. 


260 


THE   EVOLUTION    OF   MAN. 


The  ear  of  Vertebrates  develops  in  many  important 
points  similarly  to  the  eye  and  nose,  bat  yet  in  other 
respects  very  differently.172  The  organ  of  hearing  of  the 
developed  human  being  resembles  that  of  other  Mammals 
in  all  essential  particulars,  and  is  especially  similar  to  that  of 
Apes.  As  in  the  latter,  it  consists  of  two  principal  parts,  an 
apparatus  for  the  conveyance  of  sound  (external  and  middle 
ear)  and  an  apparatus  for  producing  the  sensation  of  sound 
(internal  ear).     The  outer  ear  opens  in  the  ear-shell  {concha 


Fig.  244. — Auditory  organ  of  man  (left  ear,  seen  from  the  front;  natural 

size)  :  a,  ear-shell :  b,  external  ear-canal ;  c,  drum,  or  tympanic  membrane ; 

d,  cavity  of  drum ;  e,  ear-trumpet;  /,  g,  h,  the  three  ear  bonelets  (/,  hammer ; 

g,  anvil  ;    h,  stirrup) ;    i,  ear-pouch   (utriculus) ;  fc,  the  three  semi-circular 

i  canals ;  I,  ear-sac  (sacculus) ;  m.  snail  (cochlea) ;  n,  auditory  nerve. 

auris),  situated  at  the  side  of  the  head  (Fig.  224,  a).  From 
this  the  outer  ear-canal,  which  is  usually  about  an  inch  long, 
leads  to  the  inside  of  the  head  (&).     The  inner  end  of  this 


THE   EAR.  26l 

tube  is  closed  by  the  well-known  tympanic  membrane 
or  drum  (tympanum)  ;  a  thin  membrane  of  oval  form  (c), 
placed  in  a  vertical  position,  but  slightly  inclined.  This 
membrane  separates  the  outer  ear-canal  from  the  so-called 
cavity  of  the  drum  (cavum  tympani).  This  is  a  small 
cavity  enclosed  in  the  petrous  part  of  the  temporal  bone, 
which  is  filled  with  air  and  connected  by  a  special  tube  with 
the  mouth-cavity.  This  tube  is  somewhat  longer,  but  much 
narrower  than  the  outer  ear-canal ;  it  leads  inward  and 
forward  in  an  oblique  direction  from  the  inside  wall  of  the 
tympanum  and  opens  behind  the  inner  nostrils  (or  Choana) 
into  the  upper  part  of  the  cavity  of  the  throat  (pharynx). 
This  canal  is  called  the  Eustachian  tube  (tuba  Eustachii). 
It  equalizes  the  pressure  of  the  air  in  the  tympanic 
cavity,  and  the  outer  atmospheric  air  which  enters  by 
the  ear  canal.  Both  the  Eustachian  tube  and  the  tympanic 
cavity  are  lined  by  a  thin,  mucous  membrane,  which 
is  a  direct  continuation  of  the  mucous  membrane  of  the 
throat.  Within  the  tympanic  cavity  are  the  three  bonelets 
of  the  ear,  which,  from  their  characteristic  shape,  are  called 
the  hammer,  the  anvil,  and  the  stirrup  (Fig.  244  /,  g,  h). 
The  hammer  (/)  lies  furthest  outward,  just  within  the 
tympanic  membrane;  the  anvil  (g)  is  wedged  in  between 
the  two  others,  above  the  hammer,  and  further  in  than  the 
hammer ;  and,  lastly,  the  stirrup  (h)  lies  next  to  the  anvil 
toward  the  inside,  and  touches  with  its  base  the  outer  wall 
of  the  internal  ear,  or  the  auditory  sac.  All  these  parts  of 
the  middle  and  external  ear  belong  to  the  sound-conducting 
apparatus.  Their  principal  office  is  to  convey  the  waves  of 
sound  from  without  through  the  thick  side-wall  of  the  head, 
to  the  internal  ear.     In  Fishes  these  parts  are  entirely  unre- 


262 


THE    EVOLUTION    OF   MAN. 


presented.     In  them,  the  sound-waves  are  conveyed  directly 
through  the  wall  of  the  head  itself  to  the  internal  ear. 

The  inner  apparatus,  that  which  produces  the  sensation 
of  sound,  receiving  the  sound-waves  thus  conveyed  to  it, 
consists  in  Man,  as  in  all  other  Vertebrates  (with  the  single 
exception  of  the  Amphioxus),  of  a  closed  auditory  sac  filled 
with  fluid,  and  of  an  auditory  nerve,  the  ends  of  which  are 
distributed   over  the   wall  of  this  sac.     The  vibrations  of 
the  waves  of  sound  are  conveyed  by  that  medium  to  these 
nerve-ends.      In   the    auditory   fluid   (endolymph),   which 
fills  the   labyrinth,    and   opposite  the  places  at  which  the 
auditory   nerves  enter,  are   some   small   stones,    composed 
of  a  mass  of  microscopic  calcareous  crystals  (otoliths).     The 
organs  of  hearing  of  most  Invertebrates  have  essentially 
the  same  construction.     In  them,  also,  it  usually  consists  of 
a  closed  sac  filled  with  fluid,  containing  otoliths,  and  having 
the  auditory  nerve  distributed  over  its  wall.     But  while  in 
Invertebrates   the   auditory   vesicle   is  usually  of  a   very 
simple   spherical  or  oval  form,  in  all  Amphirhina,  on  the 
contrary,  that  is,  in  all  Vertebrates  above  the  Fishes  up  to 
Man,  it  is  distinguished  by  a  very  characteristic  and  singular 
form  known  as  the  auditory  labyrinth.     This  thin  membra- 
nous labyrinth  is  enclosed  in  a  bony  envelope  of  the  same 
form,  the  osseous  labyrinth  (Fig.  245),  which  lies  within  the 
petrous  bone  of  the  skull.     The  labyrinth  in  all  Amphirhina 
is  divided  into   two   sacs.     The   larger   sac   is   called   the 
auditory  pouch  (utriculus),  and  has  three  curved  appendages, 
called  the  semi-circular  canals  (c,  d,  e) ;   the  smaller  sac  is 
called  the  auditory  sac  (sacculus),  and  is  connected  with  a 
peculiar  appendage,  which  in  Man  and  the  higher  Mammals 
is  distinguished  by  a  spiral  form,  like  the  shell  of  a  snail,  and 


DEVELOPMENT   OF   THE   EAR.  263 

hence  is  called  the  "  snail  "  {cochlea,  b).  On  the  thin  wall 
of  this  delicate  membranous  labyrinth,  the  auditory  nerve, 
which  passes  from  the  after-brain  to  the  labyrinth,  is  dis- 
tributed in  a  very  complex  manner.  It  divides  into  two 
main  branches,  the  nerve  of  the  cochlea,  and  the  nerve  of 
vestibule,  for  the  remaining  part  of  the  labyrinth.  The 
former  seems  specially  to  determine  the  quality  of  the  sound 
heard,  the  latter  its  quantity.     The  nerve  of  the  cochlea 

Fig.  245. — The  bony  labyrinth  of  the  human  ear 
(left  side) :  a,  vestibule ;  b,  cochlea ;  c,  upper  semi- 
circular canal ;  d,  posterior  semi-circular  canal ;  e, 
outer  semi-circular  canal ;  f,  fenestra  ovalis  ;  g,  fenestra 
rotunda.     (From  Meyer.) 

tells  us  the  pitch  and  quality  of  sounds,  the  nerve  of  the 
vestibule  their  strength. 

The  first  rudiment  of  this  extremely  complex  organ  of 
hearing  is  very  simple  in  the  human  embryo,  as  in  those 
of  all  other  Skulled  Animals  (Craniota) ;  it  is  a  groove-like 
depression  of  the  outer  skin  (epidermis).  At  the  back  of  the 
head,  near  the  after-brain,  at  the  upper  end  of  the  second 
gill-opening,  a  little  wart-like  thickening  of  the  horn-plate 
arises  on  each  side  (Figs.  246,  A,  fl ;  248,  g).  This  deepens 
into  a  small  groove,  and  separates  from  the  outer-skin,  just 
as  does  the  lens  of  the  eye.  (Cf.  p.  253.)  A  small  vesicle 
filled  with  fluid,  the  primitive  ear-vesicle,  is  thus  formed 
on  each  side,  immediately  below  the  horn-plate  of  the  back 
part  of  the  head ;  this  is  also  called  the  "  primary  laby- 
rinth "  (Plates  VI.  and  VII.).  As  this  separates  from  its 
original  site,  the  horn-plate,  and  grows  inward  and  down- 
ward in  the  skull,  it  changes  from  a  globular  to  a  pear- 
shaped  form  (Figs.  246,  B,  Iv ;  249,  o).     The  outer  part  has 


264 


THE   EVOLUTION    OF   MAN. 


elongated  into  a  thin  stalk,  which  at  first  opens  outward  in 
a  narrow  canal.  (Cf.  Fig.  137,/,  vol.  i.  p.  382.)  This  is  called 
the  appendage  of  the  labyrinth  recessus  labyrinthi,  Fig.  246,  for). 


Fig.  246.  —  Development  of  the  ear-labyrinth  of  a  Chick,  in  five  con- 
secutive &tages  (A-E)  (cross-sections  through  the  rudimentary  skull) :  fl, 
ear-groove ;  Iv,  ear- vesicle  ;  lr,  labyrinth  appendage ;  c,  rudiment  of  the 
cochlea ;  csp,  hind  semi-circular  canal ;  cse,  outer  semi-circular  canal ; 
jr,  jugular  vein.     (After  Reissner.) 

Figs.  247,  248.' — Head  of  an  embryonic  Chick,  on  the  third  day  of  incuba- 
tion :  247  in  front,  248  from  the  right ;  n}  rudimentary  nose  (olfactory 
groove) ;  I,  rudimentary  eye  (ocular  groove)  ;  g,  rudimentary  ear  (auditory 
groove)  ;  v,  fore-brain ;  gl,  eye-slit ;  o,  process  of  the  upper  jaw  ;  u,  process 
of  the  lower  jaw  of  the  first  gill-arch.     (After  Koelliker.) 

Fig.  249. — Primitive  brain  of  human  embryo  of  four  weeks,  in  vertical 
section,  and  the  left  half  observed  from  within :  v,  z,  m,  h,  n,  the  five  grooves  of 
the  skull  cavity  in  which  the  five  brain  bladders  are  situated  (fore,  twixt, 
mid,  hind,  and  after  brains)  ;  o,  primary,  pear-shaped  auditory  vesicle 
(showing  through);  a,  eye  (showing  through);  no,  optic  nerve;  p,  canal  of 
the  hypophysis ;  t,  central  skull-pieces.     (From  Koelliker.) 


DEVELOPMENT   OF   THE    EAR.  265 

In  lower  Vertebrates,  this  develops  into  a  peculiar  cavity 
filled  with  calcareous  crystals,  which  in  some  Primitive 
Fishes  (Selachii)  remains  permanently  open,  and  opens 
above  on  the  skull  (ductus  endolymphaticus).  In  Mam- 
mals, on  the  contrary,  the  appendage  of  the  labyrinth 
atrophies.  In  these,  it  is  of  interest  only  as  a  rudimentary 
organ,  which  has  no  longer  any  physiological  significance. 
Its  useless  remnant  traverses  the  osseous  wall  of  the  petrous 
bone  in  the  form  of  a  narrow  canal,  and  is  called  the  aque- 
duct of  the  vestibule  (aquceductus  vestibuli). 

Only  the  inner  and  lower  part  (extended  like  a  bladder) 
of  the  detached  ear-vesicle  develops  into  the  differentiated 
and  extremely- complex  structure  which  is  afterwards  known 
as  the  "secondary  labyrinth."  This  vesicle  separates  at  a 
very  early  stage  into  an  upper,  larger  section,  and  a  lower, 
smaller  section.  The  former  gives  rise  to  the  ear-pouch 
(utricidus)  with  the  three  semi-circular  canals;  from  the 
latter  proceeds  the  ear-sac  (sacculus)  with  the  "snail" 
(cochlea,  Fig.  246,  c).  The  three  semi-circular  canals 
originate  as  simple  pocket-like  processes  from  the  ear- 
pouch  (Fig.  246,  E,  cse  and  csp).  In  the  centre  of  each  of 
these  processes,  the  two  walls  coalesce,  and  separate  them- 
selves from  the  utricle,  while  their  extremities  still  commu- 
nicate with  its  cavity.  In  all  Double-nostrils  (Amphirhina) 
there  are  three  semi-circular  canals,  as  in  Man,  while  of  the 
Cyclostomi  the  Lampreys  have  but  two,  and  the  Myxinoides 
but  one  (p.  103).  The  highly-developed  structure  of  the 
"snail"  (cochlea),  which  is  one  of  the  most  delicate  and 
admirable  products  of  adaptation  in  the  mammalian  body, 
originally  develops  very  simply  as  a  bottle-like  process 
from   the   ear-sac   (sacculus).      As   Hasse   has   shown,  the 


266  THE   EVOLUTION   OF   MAN. 

various  stages  in  its  ontogenetic  development  still  exist 
permanently  side  by  side  in  the  ranks  of  the  lower  Verte- 
brates.173 Even  in  Monotremes  the  snail-like  spiral  curving 
of  the  cochlea  is  not  present ;  it  is  exclusively  characteristic 
of  the  other  Mammals  and  Man. 

The  auditory  nerve  (nervus  acusticus),  or  the  eighth 
brain-nerve, — one  of  the  main  branches  of  which  distributes 
itself  over  the  "  snail  "  (cochlea),  the  other  over  the  other 
parts  of  the  labyrinth, — is,  as  Gegenbaur  has  shown,  the 
sensory  dorsal  branch  of  a  spinal  brain-nerve,  the  motor 
ventral  branch  of  which  is  the  motor  nerve  of  the  facial 
muscles  (nervus  facialis).  Phylogenetically  it  has,  there- 
fore, originated  from  an  ordinary  skin-nerve,  and  is,  conse- 
quently, of  wholly  different  origin  from  the  optic  and 
olfactory  nerves,  which  represent  the  two  direct  processes 
of  the  brain.  In  this  respect  the  organ  of  hearing  differs 
essentially  from  the  organs  of  sight  and  of  smell.  The 
auditory  nerve  originates  from  the  cells  of  the  head-plate ; 
therefore,  from  the  skin-fibrous  layer.  From  this  also 
develop  all  the  membranous,  cartilaginous,  and  bony  cover- 
ings of  the  ear-labyrinth. 

The  development  of  the  apparatus  for  the  conveyance  of 
sound,  situated  in  the  middle  and  external  ear  of  Mammals, 
is  entirely  distinct  from  that  of  the  apparatus  of  auditory 
sensation.  It  must  be  regarded,  phylogenetically  as  well  as 
ontogenetically,  as  an  independent,  secondary  formation, 
which  only  afterwards  connects  itself  with  the  primary 
internal  ear.  Its  development  is,  however,  not  less  in- 
teresting, and  is  equally  clearly  explained  by  Comparative 
Anatomy.  In  all  Fishes,  and  in  the  yet  lower  Vertebrates, 
there  is  no  special  apparatus  for  the  conveyance  of  sound, 


(    26;    ) 

TABLE    XXXII. 

Systematic  Survey  of  the  Chief  Stages  in  the  Development 
of  the  Human  Ear. 

I.  First  Stage. 
The  auditory  nerve  is  an  ordinary  sensitive  skin-nerve,  which,  during  the 
differentiation  of  the  horn-plate,  appears  at  a  certain  point  on  the  skin  of 
the  head. 

II.  Second  Stage. 

The  differentiated  place  of  the  horn -plate,  at  which  the  auditory  nerve 
appeared,  forms  a  small  special  auditory  groove  in  the  skin,  which  has  an 
outer  orifice  in  the  appendage  called  the  "  labyrinth." 

III.  Third  Stage. 

The  auditory  groove  has  detached  itself  from  the  horn-lamina,  and  forms 
a  small  closed  auditory  vesicle  filled  with  fluid.  The  "  labyrinth-appendage  " 
becomes  rudimentary  (Aqu&ductus  vestibuli) . 

IV.  Fourth  Stage. 
The  auditory  vesicle  differentiates  into  two  connected  parts,  the  ear- 
pouch  (utriculus)  and  the  ear-sac  (sacculus).       Each  of   the  two  vesicles 
receives  a  special  main  branch  of  the  auditory  nerve. 
V.  Fifth  Stage. 
Three  semi-circular  canals  grow  from  the  ear-pouch  (as  in  all  Amphi- 
rhina). 

VI.    Sixth  Stage. 
The  "snail"  (cochlea)  grows  from  the  ear-sac  in  Fishes  and  Amphibia; 
it  is  very  insignificant,  and  is  only  developed  as  an  independent  part  in  the 
Amniota. 

VII.  Seventh  Stage. 

The  first  gill-opening  (the  blow-hole  of  Selachians)  changes  into  the 
tympanic  cavity  and  the  Eustachian  tube ;  the  former  is  externally  closed 
by  the  tympanic  membrane  (Amphibia). 

VIII.  Eighth  Stage. 

The  small  bones  of  the  ear  (ossicula  auditus)  (the  hammer  (malleus)  and 
anvil  (incus)  from  the  first  gill-arch,  the  stirrup  (stapes)  from  the  second) 
develop  from  parts  of  the  first  and  second  gill-arches. 
IX.  Ninth  Stage. 

The  external  ear  is  developed,  together  with  the  bony  ear-canal.  The 
shell  of  the  ear  is  pointed  and  movable  (as  in  most  lower  Mammals). 

X.  Tenth  Stage. 
The  ear-shell,  with  its  muscles,  becomes  disused   and  a  rudimentary 
organ.     It  is  no  longer  pointed,  but,  on  the  contrary,  has  a  curved  rim  with 
a  small  ear-flap  (as  in  Anthropoid  Apes  and  Men). 


(     268     ) 

TABLE    XXXIII. 
Systematic  Survey  of  the  Development  of  the  Human  Ear. 

I.  Survey  of  the  parts  of  the  Internal  Ear.    (Apparatus  perceptive  of  sound.) 


fl.  Stalk  of    the   primary     1.  Aqueduct    of    the    Aquaductus  vestibul i 
ear-vesicle  vestibule    {Due-    s.  Becessus  labyrinthi 

tus        endolym- 
phaticus) 


A. 

Products  of  the    <; 

Horn-plate 


Products  of  the 
Head-plate 


3.  Upper    part   of    the    2.  Ear-pouch  Utriculus 

primary  ear- vesicle      3.  Three    semi-circu-  Canales     semi-circu- 

lar,    or     curved  lares 
canals 


4,  5.  Lower    part    of   the    4.  Ear-sac 

primary  ear-vesicle       5.  "The  snail' 


6.  Auditory  nerve 


6.  Auditory  nerve 


Sacculus 

Cochlea 


Nervus  acusticus 


7.  Bony  covering  of   the     7.  Osseous  labyrinth      Labyrinthus  osseus 

membranous      laby- 
rinth 

8.  Bony   covering  of  the    8.  "  The  stony  bone  "     Os petrosum 

whole  internal  ear 


II.  Survey  of  the  parts  of  the  Intermediate  and  External  Ear.     (Apparatus  for  the 
conveyance  of  sound.) 


Products  of  the 
first 

Gill-opening 


D.  . 
Products  of  the 
first  two 

Gill-arches 


Product  of  the 
Head-plate 


Product  of  the 
Skin-covering 


9.  Inner  part  of  the  first      9.  Eustachian  tube        Tuba  Eustachii 
gill-opening 

10.  Central  pirt  of  the  first     10.  Tympanic  cavity      Cavum  tympani 
gill-opening  (Interior  of  the 

drum) 

1.1.  Closed  part  of  the  first     11.  Tympanic    mem-    Membrana  tympani 
gill-opening  brane  (Head   of 

the  drum) 

12.  Upper    part    of     the    12.  Stirrup  (First    Stapes 

second  gill-arch  bonelet    of    the 

ear) 

13.  Upper  part  of  the  first     13.  Anvil        (Second    Incus 

gill-arch  bonelet    of    the 

ear) 

14.  Central  part  of  the  first     14.  Hammer     (Third    Malleus 

gill-arch  bonelet    of    the 

ear) 


15.  Tympanic  circle  15.  Bony  outer  audi-    Meatus 

(Annulus  tympanicus)  tory  passage  osseus 


16.  Circular   membranous    16.  Ear-shell  Concha  a ur is 

fold  at  the  closed  part 
of  the  first  gill- 
opening 

17.  Rudimentary  ear-    Musculi  concJue 
muscles 


DEVELOPMENT   OF   THE   EAR.  269 

no  external  and  middle  ear ;  in  these  animals  there  is  only 
a  labyrinth,  an  internal  ear,  situated  within  the  skull.  The 
tympanic  membrane,  its  cavity,  and  all  the  connected  parts 
are  unrepresented.  The  middle  ear  first  develops  in  the 
Amphibian  class,  in  which  a  tympanic  membrane,  a  tym- 
panic cavity,  and  an  Eustachian  tube  are  first  found.  All 
these  essential  parts  of  the  middle  ear  develop  from  the  first 
gill-opening,  with  its  surrounding  parts,  which  in  the  Pri- 
mitive Fishes  (Selachii)  remains  through  life  as  an  open 
blow-hole,  situated  between  the  first  and  second  gill-arches. 
In  the  embryos  of  higher  Vertebrates  it  closes  in  the  centre, 
the  point  of  concrescence  forming  the  tympanic  membrane. 
The  remaining  outer  part  of  the  first  gill-opening  is  the 
rudiment  of  the  outer  ear-canal.  From  the  inner  part 
originates  the  tympanic  cavity,  and  further  inward,  the 
Eustachian  tube.  In  connection  with  these,  the  three  bone- 
lets  of  the  ear  develop  from  the  first  two  gill-arches ;  the 
hammer  and  anvil  from  the  first,  and  the  stirrup  from 
the  upper  end  of  the  second  gill-arch.174 

Finally,  as  regards  the  external  ear,  the  ear-shell  (concha 
auris),  and  the  outer  ear-canal,  leading  from  the  shell  to  the 
tympanic  membrane — these  parts  develop  in  the  simplest 
way  from  the  skin-covering  which  borders  the  outer  orifice 
of  the  first  gill-opening.  At  this  point  the  ear-shell  rises  in 
the  form  of  a  circular  fold  of  skin,  in  which  cartilage  and 
muscles  afterwards  form  (Fig.  238,  p.  247).  This  organ  is 
also  limited  to  Mammals.  Among  them,  it  is  originally 
wanting  only  in  the  lowest  division,  in  the  Beaked  Animals, 
(Monotrema).  In  the  others,  on  the  contrary,  it  appears 
in  very  different  stages  of  development  and  partly  also  of 
atrophy.      The    ear-shell   has   atrophied    in    most   aquatic 


270  THE  EVOLUTION   OF   MAN. 

Mammals.  Most  of  these  have  even  lost  it  entirely ;  this 
is  so,  for  example,  in  the  Sea-cows  and  Whales,  and  most 
Seals.  On  the  other  hand,  in  the  great  majority  of  Pouched 
Animals  (Marsupialia)  and  Placental  Animals  (Placentalia), 
the  ear-shell  is  well  developed,  receives  and  concentrates  the 
waves  of  sound,  and  is  provided  with  a  highly-developed 
muscular  apparatus,  by  means  of  which  it  can  be  turned 
freely  to  all  sides,  and  at  the  same  time  can  be  changed  in 
form.  Every  one  must  have  noticed  how  strongly  and  freely 
our  domestic  Mammals,  Horses,  Cows,  Dogs,  Rabbits,  etc., 
can  "  prick  "  their  ears,  erect  them  and  turn  them  in  different 
directions.  Most  Apes  yet  retain  the  power  of  doing  this, 
and  our  ancient  Ape  progenitors  could  also  do  it.    The  more 


Frc  250. Rudimentary  ear-muscles   on   the  human  skull :    a,  upward 

muscle  (m.  attollens) ;  h,  forward  muscle  (m.  attrahens) ;  c,  backward  muscle 
(m.  retrahens) ;  d,  larger  muscle  of  the  helix  (m.  helicis  major) ;  e,  smaller 
muscle  of  the  helix  (m.  helicis  minor) ;  /,  muscle  of  the  tragus  (m.  tragicus) ; 
g,  muscle  of  the  antitragus  (m.  antitragicus) .     (After  H.  Meyer.) 

recent  Ape  ancestors,  common  to  Men  and  to  the  Anthropoid 
Apes  (Gorilla,  Chimpanzee,  etc.),  discontinued  the  habit  of 
moving  their  ears,  and  hence  the  motor  muscles  gradually 


THE   EAR  IN   MAN   AND  APES.  2"J\ 

became  rudimentary  and  useless.  We  still,  however,  possess 
them  (Fig.  250).  A  few  individual  men  can  even  move  their 
ears  forward  or  backward  a  little  by  the  use  of  the  forward 
muscle  (b)  and  the  backward  muscle  (c) ;  and  by  long- 
practice  these  motions  can  be  gradually  increased.  On  the 
other  hand,  no  man  is  able  to  erect  the  ear-shell  by  the 
upward  muscle  (a),  or  to  change  its  form  by  the  little  inner 
muscles  of  the  ear  (d,  e,  f,  g).  These  muscles,  which  were 
very  useful  to  our  ancestors,  have  become  entirely  un- 
important to  us.     This  is  equally  true  of  Anthropoid  Apes. 

We  also  share  only  with  the  higher  Anthropoid  Apes — 
the  Gorilla,  Chimpanzee,  and  Orang — the  characteristic  form 
of  our  human  ear-shell,  especially  the  rolled  edge,  the  helix, 
and  the  ear-flap.  The  lower  Apes,  like  all  other  Mammals, 
have  pointed  ears  without  the  helix,  and  without  ear-flaps. 
Darwin  has,  however,  shown  that  in  some  men  a  short, 
pointed  process,  not  occurring  in  most  individuals,  is  per- 
ceptible at  the  upper  part  of  the  folded  rim  of  the  ear.  In 
some  few  individuals,  this  process  is  very  well  developed. 
It  can  only  be  explained  as  the  remnant  of  the  original 
point  of  the  ear  which,  in  consequence  of  the  folding  of  the 
edge  of  the  ear,  has  been  bent  forward  and  inward. 
(Of.  the  similarly  folded  ear  in  the  embryo  of  the  Pig 
and  Cow,  Plate  VII.  Fig.  H  III.  and  G  in.)  On  carefully 
comparing  the  ear-shells  of  Man  and  of  the  various  Apes  in 
this  particular,  we  find  that  they  form  a  connected  series  of 
retrograde  steps.  In  the  common  catarhine  ancestors  of  the 
Anthropoids  and  of  Man,  this  retrogression  began  with  the 
folding  down  of  the  ear-shell.  In  consequence  of  this,  the 
ear-edge  was  formed  on  which  that  significant  corner 
appears,  the  last  trace  of  the  free  prominent  point  of  the  ear 
35 


272  THE   EVOLUTION   OF  MAN. 

in  our  older  Ape  ancestors.  Thus  it  is  possible  even  here, 
with  the  help  of  Comparative  Anatomy,  to  trace  this  human 
organ  from  the  similar  but  more  highly-developed  organ  of 
the  lower  Mammals,  with  certainty.  At  the  same  time,  Com- 
parative Physiology  shows  us  that  this  organ  is  of  more 
or  less  high  physiological  value  to  the  latter,  while  in 
Anthropoids  and  Man  it  is  a  useless  rudimentary  organ. 
Men  with  their  ears  cut  off  can  hear  as  well  as  they  did 
before.  The  conveyance  of  sound  is  not  affected  by  the  loss 
of  the  ear-shell.  This  explains  the  great  diversity  in  the 
form  and  size  of  the  ear-shell  in  different  persons ;  it  shares 
this    high   degree    of   variability   with    other   rudimentary 


organs 


175 


CHAPTER  XXII. 

DEVELOPMENT   OF   THE   ORGANS   OP   MOTION. 

The  Motive  Apparatus  of  Vertebrates. — These  are  constituted  by  the 
Passive  and  Active  Organs  of  Motion  (Skeleton  and  Muscles). — The 
Significance  of  the  Internal  Skeleton  of  Vertebrates. — Structure  of  the 
Vertebral  Column. — Formation  and  Number  of  the  Vertebrae. — The  Ribs 
and  Breast-bone. — Germ-history  of  the  Vertebral  Column. — The  Noto- 
chord. — The  Primitive  Vertebral  Plates. — The  Formation  of  the  Meta- 
mera. — Cartilaginous  and  Bony  Vertebra?. — Intervertebral  Discs. — 
Head-skeleton  (Skull  and  Gill-arches). — Vertebral  Theory  of  the  Skull 
(Goethe  and  Oken,  Huxley  and  Gegenbaur). — Primitive  Skull,  or 
Primordial  Cranium. — Its  Formation  from  Nine  or  Ten  Coalescent 
Metamera. — The  Gill-arches  (Ribs  of  the  Head). — Bones  of  the  Two 
Pairs  of  Limbs. — Development  of  the  Five-toed  Foot,  adapted  for 
Walking,  from  the  Many-toed  Fin  of  the  Fish. — The  Primitive  Fin 
of  the  Selachians  (Archipterygiwm  of  Gegenbaur). — Transition  of  the 
Pinnate  into  the  Semi-pinnate  Fin. — Atrophy  of  the  Rays  or  Toes 
of  the  Fins. — Many-fingered  and  Five-fingered  Vertebrates. — Com- 
parison of  the  Anterior  Limbs  (Pectoral  Fins)  and  the  Posterior  Limbs 
(Ventral  Fins). — Shoulder  Girdle  and  Pelvis  Girdle. — Germ-history  of 
the  Limbs. — Development  of  the  Muscles. 

"  In  forming  his  estimate  of  my  entire  theory,  the  reader  may  begin  with 
the  details  and  examine  the  fundamental  facts  on  which  I  base  my  con- 
clusions. But  it  is  equally  necessary  to  connect  the  detached  facts,  and 
estimate  their  bearing  on  the  whole.  Ho  who  in  the  world  of  organisms  sees 
only  disconnected  existences,  in  which  some  organic  similarities  appear  as 


274  THE   EVOLUTION   OF   MAN. 

accidental  coincidences,  will  remain  a  stranger  to  the  results  of  this 
investigation  ;  not  mei'ely  because  he  does  not  comprehend  the  conclu- 
sions, but  principally  because  the  significance  of  the  facts  on  which  they 
are  grounded,  escapes  him.  A  fact  in  itself  is  no  more  a  scientific  result, 
than  a  mere  collection  of  facts  is  a  science.  That  which  makes  a  science 
of  these  facts,  is  their  combination  by  that  organizing  mental  faculty  which 
determines  the  relations  of  the  facts  to  each  other." — Karl  Gegenbaur 
(1872). 

Among  those  features  of  the  organization  which  are  specially 
characteristic  of  the  vertebrate  tribe  as  such,  the  peculiar 
arrangement  of  the  motive  apparatus,  or  "  locomotorium," 
undoubtedly  occupies  a  principal  place.  As  in  all  the 
higher  animals,  the  active  organs  of  motion,  the  muscles, 
form  the  most  important  part  of  this  apparatus  ;  these  are 
the  fleshy  bands  which,  by  means  of  their  peculiar  contrac- 
tibility,  of  their  power  of  contracting  and  shortening,  move 
the  various  parts  of  the  body,  and  thus  change  the  position 
of  the  entire  body.  The  arrangement  of  these  muscles  is, 
however,  entirely  peculiar  in  Vertebrates,  and  differs  from 
the  arrangement  common  to  all  Invertebrates. 

In  most  lower  animals,  especially  in  Worms,  we  find 
that  the  muscles  form  a  simple,  thin  fiesh-layer  immediately 
below  the  outer  skin-covering.  This  "  skin-muscle  pouch  " 
is  most  intimately  connected  with  the  skin  itself,  and  the 
same  feature  occurs  in  the  tribe  of  the  Soft-bodied  Animals 
(Mollusca).  In  the  great  group  of  the  Articulated  Animals 
(ArthroiJoda),  in  the  Grab,  Spider,  Centipede,  and  Insect 
classes,  we  also  find  a  similar  feature,  but  with  the  difference 
that  in  these  the  skin-covering  forms  a  hard  coat  of  mail ; 
an  inflexible  skin-skeleton,  formed  of  chitine,  and  often  of 
carbonated  chalk.  This  outer  chitinous  coat  of  mail  is 
jointed  in  a  great  variety  of  ways  both  on  the  trunk  and 


THE   SKELETON.  275 

on  the  limbs  of  Articulated  Animals,  and  the  muscular 
system,  the  contractile  fleshy  bands  of  which  are  attached 
to  the  inside  of  the  chitinous  tubes,  is  correspondingly 
jointed  in  an  extremely  varied  manner.  The  case  is  exactly 
reversed  in  Vertebrates.  In  these  alone  an  internal  hard 
skeleton  develops ;  an  inner  cartilaginous  or  bony  frame 
to  which  the  fleshy  muscles  are  externally  attached,  and  in 
which  they  find  a  firm  support.  This  bony  frame  forms  a 
combined  lever-apparatus,  a  passive  apparatus  of  motion. 
The  hard  parts  of  this,  the  arms  of  the  lever,  or  the 
bones,  are  moored  against  each  other  by  the  active  movable 
muscular  bands,  as  by  hawsers.  This  admirable  locomotive 
apparatus,  and  especially  its  firm  central  axis,  the  vertebral 
column,  is  quite  peculiar  to  Vertebrates,  on  account  of  which 
the  whole  group  has  long  been  called  that  of  Vertebrates. 

This  internal  skeleton,  notwithstanding  the  similarity  of 
its  first  rudiment,  has,  however,  developed  so  variously  and 
characteristically  in  the  different  vertebrate  classes,  and  in 
the  higher  classes  forms  so  complex  an  apparatus,  that 
Comparative  Anatomy  finds  one  of  its  richest  mines  in  this 
feature.  This  was  recognized  as  long  ago  as  the  beginning 
of  the  century  by  the  older  Natural  Science,  which  at  once 
seized  these  very  welcome  materials  with  peculiar  pleasure. 
That  science  also,  which  is  now  called  in  the  higher  and 
more  philosophical  sense,  "  Comparative  Anatomy,"  has 
reaped  its  richest  harvest  from  this  field.  The  Comparative 
Anatomy  of  the  present  day  has  studied  the  skeleton  of 
Vertebrates  more  thoroughly,  and  revealed  the  laws  of  its 
formation  more  successfully,  than  has  been  the  case  with 
any  other  system  of  organs  of  the  animal  body.  Here  the 
well-known    and    oft-quoted    passage,    in    which    Goethe 


2j6  THE   EVOLUTION   OF   MAN. 

summed  up  the  general  result  of  his  investigations  in  Mor- 
phology is  especially  appropriate : 

"  All  forms  have  a  resemblance ;  none  is  the  same  as  another, 
And  their  chorus  complete  points  to"  a  mystical  law."  * 

Now  that,  by  the  Theory  of  Descent,  we  have  discovered 
this  "  mystical  law,"  have  solved  this  "  sacred  enigma,"  now 
that  we  can  explain  the  similarity  of  forms  by  Heredity, 
and  their  dissimilarity  by  Adaptation,  we  can  find  no 
weapon  in  the  whole  rich  arsenal  of  Comparative  Anatomy 
which  defends  the  truth  of  the  Theory  of  Descent  more 
powerfully  than  the  comparison  of  the  internal  skeletons 
of  the  various  Vertebrates.  We  may,  therefore,  expect 
a  priori  that  such  comparison  is  of  special  importance  in 
our  History  of  the  Evolution  of  Man.  The  inner  vertebrate 
skeleton  is  one  of  those  organs  as  to  the  Phylogeny  of 
which  Comparative  Anatomy  affords  us  conclusions  far 
more  important  and  deeper  than  those  to  be  gained  from 
its  Ontogeny.176 

More  than  any  other  system  of  organs,  the  internal 
skeleton  of  Vertebrates,  when  studied  comparatively,  clearly 
and  immediately  impresses  the  observer  with  the  necessity 
of  the  phylogenetic  connection  between  these  allied  and  yet 
very  varied  forms.  A  thoughtful  comparison  of  the  bony 
frame  of  Man  with  that  of  other  Mammals,  and  of  these 
again  with  that  of  lower  Vertebrates,  is  alone  sufficient  to 
afford  conviction  of  the  true  tribal  relationship  of  all 
Vertebrates.  All  the  separate  parts  of  which  this  bony 
frame  is  composed  appear  in  other  Mammals,  in  a  great 

*  "  Alle  Gestalten  sind  ahnlicb,  doch  keine  gleichet  der  andern; 
Und  so  deutet  der  Chor  auf  ein  geheimes  Gesetz." 


IMPORTANCE  OF  THE  SKELETON.  277 

variety  of  forms  indeed,  but  yet  in  the  same  characteristic 
arrangement  and  relative  position ;  and  if  the  comparison 
of  the  anatomical  conditions  of  the  skeleton  is  carried  out 
below  Mammals,  we  can  prove  that  a  direct  and  uninter- 
rupted connection  exists  throughout  between  these  various 
forms  which  are  apparently  so  utterly  unlike,  and  can 
finally  be  traced  from  a  most  simple,  common,  fundamental 
form.  These  facts  alone  must  fully  convince  every  ad- 
herent of  the  Theory  of  Development  that  all  Vertebrates, 
including  Man,  must  be  traced  from  a  single  common 
parent-form,  from  a  Primitive  Vertebrate ;  for  the  mor- 
phological features  of  the  inner  skeleton,  and  of  the  mus- 
cular system  which  stands  in  the  closest  correlative  rela- 
tions to  it,  are  of  such  a  kind  that  it  is  quite  impossible 
to  conceive  a  polyphyletic  origin,  a  descent  from  several 
different  root-forms.  It  is  impossible,  on  mature  reflection, 
to  accept  the  theory  that  the  vertebral  column  with  its 
various  appendages,  or  the  skeleton  of  the  limbs  with  their 
variously  differentiated  parts,  could  have  originated  on 
several  occasions  during  the  course  of  the  earth's  history, 
and  that,  consequently,  the  various  Vertebrates  must  be 
referred  in  various  lines  of  descent  from  Invertebrates. 
Indeed,  it  is  exactly  in  this  point  that  Comparative  Anatomy 
and  Ontogeny  irresistibly  drive  us  to  the  monophyletic 
conclusion,  that  the  human  race  is  a  very  recent  offshoot 
of  the  same  great  single  trunk,  from  branches  of  which  all 
other  Vertebrates  have  also  sprung. 

In  order  to  obtain  a  view  of  the  outlines  of  the  develop- 
ment of  the  human  skeleton,  we  must  first  take  a  general 
survey  of  its  arrangement  in  the  developed  Man.  (Cf. 
Table  XXXIV.  and  Fig.  251,  the  human  skeleton  from  the 


(    2;3    ) 
TABLE    XXXIY. 

Systematic  Survey  of  the  Arrangement  of  the  Human  Skeleton. 


A.  Central  Skeleton,  or  Axial  Skeleton.     Spine. 


A. a.  Vertebral  Bodies  and  Upper  Arches. 

1.  Skull  j    la.  Pre-vertebral  skull 
(Cranium)  \    2  6.  Vertebral  skull 

f  1  Neck  vertebra: 

2.  Vertebral    |  12  Chest 
column     -i,    5  Hip  „ 

(Columna   j    5  Vertebra?  of  the  sacrum 
vertebralis)  [_  4         „        „    „  tail  (coccyx) 


A.b.  lower  Vertebral  Arches. 
1.  Products  of  the  gill-    Producta    arcuum 


arches 


branch  iali  am 


r 


Ribs    and    breast-    Costa;  et  sternum 
bone 


B.  Bones  connecting  the  Extremities. 


B.a.  Pones  connecting  the  Anterior  Limbs: 
Pones  of  the  Shoulder. 

1.  Shoulder-blade  Scapula 

(2.  Primitive  key-bone  Procoracoidesf) 

(3.  Raven  I  one  Coracoides      f) 

4.  Collar-bone,  or  key -bone  Clavicula 


B.b.  Pones  connecting  the  Lower  Limbs: 
Pones  of  the  Pelvis. 

1.  Intestinal  bone  Os  ilium 

2.  Pubic  bone  Os  pubis 

3.  Hip-bone  Os  itchi 


C.  Jointed  Skeleton  of  the  Limbs. 


C.a.  Slcelcton  of  the  Fore  Limbs. 

C.  b.  Skeleton  of 

he  Hind  Limbs. 

I.  Fikst  Division  : 

Ul'PER    A  KM. 

I.  First  Division  :  Thigh. 

1.  Upper  arm  bone 

Humerus 

1.  Thigh-bone 

Femur 

II.  Second  Division 

Lower  Arm. 

II.  Second  Division:  Leg. 

2.  Spoke-bone 

3.  Ell-bone 

Radius 
Vina 

2.  Shin-bone 

3.  Calf-bone 

Tibia 
Fibula 

III.  Thikd  Division  :  Hand. 

III.  Third  Division  :  Foot. 

III.  A.  Wrist 

Carpus 

III.  Ankle 

Tarsus 

Original  parts. 

/  a.  Radical 
1  b.  Intermedium 
j  c.  Ulnar 
'  Id.  Central 

Modified  parts 

=  Scaphoideum 
=  Lunatum, 
=  Triquetrum 
=  Intermedium 

tl 

Original  parts. 
/  a.  Tibial 
\  b.  Intermedium 
j  c.   Fibular 
\d.  Central 

Modified  parts. 
}  =  Astragalus 

—  Calcaneus 
=  Naviculars 

i  e    Carpal      T. 
)/.       „        II. 

)g.     ..     in- 
U.     „     iv.  +  v. 

=  Trapezium 
=  Trapezoides 
z=  Capitatum 
=  Hamatum 

.'  e.  Tarsal     I. 
/.       „        II. 

\g.     „     in. 

\h.      „      IV. +  V. 

—  Cuneiform     I. 
=          ,,            II. 
=          „          III. 
=  Cuboides 

III.  P.  Palm  of  the  Hand 

Metacarpus 

C5-) 

III.  P.  Sole  of  the  Foot 

Metatarsus  (5) 

III.  C.  Five  Fingers 
(14  bones 

JJiijiti 
Phalanges) 

III.  C.  Five  Toes 
(14  bones 

j  n't/ m 

Phalanges) 

HUMAN   SKELETON. 


279 


Fig.  251. 


Fig.  252. 


28o 


THE   EVOLUTION   OF  MAN. 


Fig.  253.— 
Human  vertebral 
column  (in  an  up- 
right position ; 
from  the  right 
side).  (After  H. 
Meyer.) 


right  side  (without  arms);  Fig.  252,  the 
entire  skeleton  from  the  front.)  In  Man, 
as  in  all  other  Mammals,  the  skeleton  is 
primarily  distinguishable  into  the  axial 
skeleton,  or  spine,  and  the  skeleton  of  the 
appendages,  or  the  bony  frame  of  the  limbs. 
The  spine  consists  of  the  vertebral  column 
and  of  the  skull ;  the  latter  being  the  pecu- 
liarly modified  anterior  part  of  the  former. 
The  ribs  are  the  appendages  of  the  vertebral 
column ;  the  tongue-bone  (os  linguce),  the 
lower  jaw,  and  the  other  products  of  the 
gill-arches,  are  those  of  the  skull.  The 
skeletons  of  the  two  pairs  of  limbs,  or  ex- 
tremities, are  composed  of  two  different 
parts  :  of  the  bony  frame  of  the  actual,  pro- 
minent extremities,  and  of  the  inner  girdle 
skeleton,  by  which  the  limbs  are  attached 
to  the  vertebral  column.  The  girdle  skele- 
ton of  the  arms  (or  fore  limbs)  is  the 
shoulder  girdle ;  the  girdle  skeleton  of  the 
legs  (or  the  hind  limbs)  is  the  pelvic 
girdle. 

The  bony  vertebral  column  in  human 
beings  (cohimna  vertebralis,  or  vertebra- 
rium,  Fig.  253)  is  composed  of  thirty-three 
or  thirty-four  circular  pieces  of  bone,  which 
lie  one  behind  the  other  (one  above  the 
other  in  the  usual  upright  position  of 
man).  These  bones  (vertebra?)  are  sepa- 
rated from  each  other  by  elastic  cushions, 


DEVELOPMENT  OF  THE  SKELETON. 


28l 


the  intervertebral  discs  (I'igamenta  intervertebralia),  and 
at  the  same  time,  are  connected  by  joints,  so  that  the 
entire  vertebral  column  forms  a  firm  and  solid  axis,  which 
is,  however,  flexible  and  elastic,  capable  of  moving  freely 
in  all  directions.  In  the  various  regions  of  the  trunk, 
the  vertebrae  differ  in  form  and  connection,  so  that  the 
following  are  distinguished  in  the  human  vertebral  column, 
beginning  from  above  :  seven  neck- vertebrae,  twelve  breast- 
vertebrae,  five  lumbar-vertebrae,  five  cross-vertebrae,  and 
four  to  five  tail-vertebrae.     The  uppermost,  those  directly  in 


Fig.  254. — Third  neck-vertebra  of  man. 
Fig.  255. — Sixth  breast. vertebra  of  man. 
Fig.  256. — Second  lumbar-vertebra  of  man. 


contact  with  the  skull,  are  the  neck-vertebras  (Fig.  254), 
and  are  distinguished  by  a  hole  found  in  each  of  the 
two  lateral  processes.  There  are  seven  neck-vertebrae  in 
Man,  as  in  nearly  all  other  Mammals,  whether  the  neck 
is  long,  as  in  the  Camel  and  the  Giraffe,  or  short,  as  in  the 
Mole  and  the  Hedgehog.  The  fact  that  the  number  of  these 
neck-vertebrae  is  always  seven, — and  there  are  but  few 
exceptions  (explicable  by  adaptation), — is  a  strong  argu- 
ment for  the  common  descent  of  all  Mammals ;  it  can  only 
be  accounted  for  as  a  strict  transmission  from  a  common 


282  THE   EVOLUTION   OF  MAN. 

parent-form,  from  some  Promammal  which  had  seven  neck- 
vertebras.  If  each  animal  species  had  been  a  distinct  crea- 
tion, it  would  have  been  far  more  to  the  purpose  to  have 
furnished  the  long-necked  Mammalia  with  a  larger,  and  the 
short-necked  with  a  smaller  number  of  neck-vertebras.  The 
neck- vertebras  are  immediately  followed  by  those  of  the  breast 
or  thorax,  which,  in  Man  and  most  other  Mammals,  number 
twelve  or  thirteen  (usually  twelve).  Attached  to  the  sides 
of  each  breast-vertebra  (Fig.  255)  is  a  pair  of  ribs — long 
curved  processes  of  bone  lying  in  and  supporting  the  wall  of 
the  thorax.  The  twelve  pairs  of  ribs,  with  the  connecting 
intercostal  muscles  and  the  breast-bone  (sternum)  constitute 
the  breast -body  (thorax,  Fig.  252,  p.  279).  In  this  elastic 
and  yet  firm  thorax  lie  the  double  lung,  and  between  the 
two  halves  of  this,  the  heart.  The  chest-vertebras  are 
followed  by  a  short  but  massive  section  of  the  vertebral 
column,  formed  by  five  large  vertebras.  These  are  the 
lumbar- vertebras  (Fig.  256),  which  bear  no  ribs  and  have 
no  perforations  in  their  lateral  processes.  Next  comes  the 
cross-bone  (sacrum),  which  is  inserted  between  the  two 
halves  of  the  pelvic  girdle.  This  cross-bone  consists  of  five 
fixed  and  amalgamated  cross-vertebras.  Last  comes  a  small 
rudimentary  tail- vertebral  column,  the  rump-bone  (coccyx). 
This  bone  consists  of  a  varying  number  (usually  four,  more 
rarely  three  or  five)  of  small  aborted  vertebras ;  it  is  a 
useless  rudimentary  organ,  retaining  no  physiological  sig- 
nificance either  in  Man  or  in  the  Tail-less  Apes  or  Anthro- 
poids. (Of.  Figs.  204-208.)  Morphologically  it  is,  however, 
very  interesting,  as  affording  incontrovertible  evidence  of 
the  descent  of  Man  and  of  Anthropoids  from  Long- tailed 
Apes.      For    this    assumption     affords    the     only    possible 


THE   VERTEBRA. 


283 


explanation  of  this  rudimentary  tail.  In  the  human 
embryo,  indeed,  during  the  earlier  stages  of  germ-history, 
the  tail  projects  considerably.  (Cf.  Plate  VII.  Fig.  M  II., 
and  Figs.  123,  s,  124,  s,  vol.  i.  p.  370.)  It  afterwards  becomes 
adherent,  and  is  no  longer  externally  visible.  Yet  traces 
of  the*  aborted  tail- vertebrae,  as  well  as  of  the  rudimentary 
muscles,  which  formerly  moved  them,  persist  throughout  life. 
According  to  the  earlier  anatomists  the  tail  in  the  female 
human  being  has  one  vertebra  more  than  that  of  the  male 
(four  in  the  latter,  five  in  the  former).177 


Number  of  Yertebrce  in  various  Catarhini. 


Tail- 
less 


(Man  (Fig.  208)    

Orang  (Fig.  205)    

Gibbon  (Fig.  204)  

Gorilla  (Fig.  207)  

Chimpanzee  (Fig.  20fi) 


/Mandril  (Mormon  choras) 

Drill  (Mormon  leucophceus)   ... 

Tailed  \  Rhesus  (Inuus  rhesus)   

Sphinx  (Papio  sphinx)  

Simpai  (Semnopithecus  inelus) 


Chest 
Keck  or  tfto- 
Verte-  racic 
bra.  Yerte- 
brce. 


12 
12 
13 
13 

14 


13 
12 
12 
13 
12 


Lum- 
bar 

Yerte- 
brce. 


sacral 
Yerte- 
brce. 


Tail 

Yerte- 
brce. 


5 

8 

18 

24 

31 


Tutal. 


33 
33 
32 
33 
34 


34 
37 
46 
53 

60 


The  number  of  vertebrae  in  the  human  vertebral  column 
is  usually  thirty-three  in  all ;  but  it  is  an  interesting  fact 
that  this  number  frequently  varies,  one  or  another  vertebra 
failing,  or  a  new,  supernumerary  vertebra  inserting  itself. 
Not  unfrequently,  also,  a  rib,  capable  of  free  motion,  forms 
on  the  last  neck-vertebra  or  on  the  first  lumbar- vertebra,  so 
that  thus  there  are  thirteen  breast,  and  six  neck,  or  four 
Lumbar  vertebra;.  In  this  way  contiguous  vertebrae  in  the 
different  sections  of  the  vertebral  column  may  replace  each 


284  THE   EVOLUTION   OF  MAN. 

other.  On  the  other  hand,  the  above  comparison  of  the 
number  of  vertebrae  in  different  tail-less  and  tailed  Catarhines 
shows  considerable  fluctuations  in  these  numbers  even  in 
this  one  family.178 

To  understand  the  history  of  the  development  of  the 
human  vertebral  column,  we  must  now  study  the  form  and 
combination  of  the  vertebras  in  somewhat  greater  detail. 
The  main  outline  of  each  vertebra  is  that  of  a  signet  ring 
(Figs.  254-256).  The  thicker  part,  which  faces  the  ventral 
side,  is  called  the  body  of  the  vertebra,  and  it  forms  a  short 
disc  of  bone ;  the  thinner  forms  a  semi-circular  arch — the 
vertebral  arch,  which  is  turned  toward  the  dorsal  side  of  the 
body.  The  arches  of  all  the  consecutive  vertebrae  are  so  con- 
nected by  thin  ligaments  (ligamenta  intercruralia)  that  the 
space  enclosed  by  them  all  in  common  forms  a  long  canal. 
In  this  spinal,  vertebral  canal  lies,  as  we  have  seen,  the  hind 
portion  of  the  central  nervous  system,  the  spinal  marrow. 
The  front  part  of  this,  the  brain,  is  enclosed  in  the  skull- 
cavity,  and  hence  the  skull  itself  is  merely  the  anterior 
section  of  the  vertebral  column,  modified  in  a  peculiar  way. 
The  base  or  ventral  side  of  the  bladder-shaped  brain-capsule 
was  originally  formed  by  a  number  of  coalescent  vertebral 
bodies,  the  amalgamated  upper  vertebral  arches  of  which 
formed  the  arched  or  ventral  side  of  the  skull. 

While  the  firm,  massive  vertebral  bodies  constitute  the 
true  central  axis  of  the  skeleton,  the  dorsal  arches  serve  to 
enclose  and  protect  the  central  marrow.  Analogous  arches 
also  develop  on  the  ventral  side  as  a  protection  for  the 
thoracic  and  abdominal  viscera.  These  inferior  or  ventral 
vertebral  arches,  proceeding  from  the  ventral  side  of  the 
vertebral  bodies,  form  a  canal  in  many  low  Vertebrates  in, 


NATURE  OF  THE  VERTEBRAE.  285 

which  are  enclosed  the  large  blood-vessels  on  the  under 
surface  of  the  vertebral  column — the  aorta  and  the  tail  vein. 
In  higher  Vertebrates  most  of  these  inferior  vertebral  arches 
are  lost  or  become  merely  rudimentary.  But  in  the  breast 
section  of  the  vertebral  column  they  develop  into  strong, 
independent  bony  arches,  the  ribs  (costce).  The  ribs  are,  in 
fact,  merely  large  vertebral  arches  which  have  become 
independent,  and  have  broken  their  original  connection 
with  the  vertebral  bodies.  The  gill  arches,  of  which  we 
have  spoken  so  often,  are  of  similar  origin ;  they  are  actual 
head-ribs  in  the  strictest  sense — processes  which  have 
actually  originated  from  the  lower  arches  of  the  skull- 
vertebroe,  and  which  correspond  with  the  ribs.  Even  the 
mode  of  connection  of  the  right  and  left  halves  of  the  arches 
on  the  ventral  side  is  the  same  in  both  instances.  The 
chest  is  closed  in  front  by  the  intervention,  between  the 
upper  ribs,  of  the  breast-bone  (sternum) — a  single  bone 
originating  from  two  corresponding  side-halves.  The  gill- 
body  is  also  closed  in  front  by  the  intervention  of  a  single 
piece  of  bone — the  copula  lingualis. 

In  now  turning  from  this  anatomical  examination  of  the 
constitution  of  the  vertebral  column  to  the  question  of  its 
development,  I  may,  as  regards  the  first  and  most  important 
features  in  the  evolution,  refer  the  reader  to  the  explanation 
already  given  of  the  germ-history  of  the  vertebral  column 
(Chap.  XII,  vol.  i.  pp.  3G9-378).  In  the  first  place,  it  is  ne- 
cessary to  recollect  the  important  fact  that  in  Man,  as  in  all 
other  Vertebrates,  a  simple,  unarticulated  cartilaginous  rod 
at  first  occupies  the  place  of  the  articulated  vertebral  column. 
This  firm  but  flexible  and  elastic  cartilaginous  rod  is  the 
well-known  notochord  (chorda  dorsalis).     In  the  lowest  Ver- 


286 


THE   EVOLUTION   OF   MAN. 


tebrate,  the  Amphioxus,  this  persists  throughout  life  in  this 
very  simple  form,  and  permanently  constitutes  the  whole 
internal  skeleton  (Fig.  151,  i,vo\.  i.  p.  420  ;  Plate  XI.  Fig.  15). 
But  even  in  the  Mantle  Animals  (Tunicata),  the  nearest 
invertebrate  allies  of  Vertebrata,  we  find  this  same  noto- 
chord; transitorily  in  the  transient  larval  tail  of  Ascidia 
(Plate  X.  Fig.  5,  ch) ;  permanently  in  the  Appendicularia 
(Fig.  162).  The  Mantle  Animals,  as  well  as  the  Acrania, 
have  undoubtedly  inherited  the  notochord  from  a  common 
worm-like  parent-form,  and  these  primaeval  worm  ancestors 
are  the  Chorda  Animals  (Chordonia,  p.  91). 

Long  before  any  trace  of  a  skull,  limbs,  etc.,  appears  in  the 
human  embryo  or  in  that  of  any  of  the  higher  Vertebrates — 
in  that  early  stage  when  the  whole  body  is  represented  only 
..<$     by  the  lyre-shaped  germ-disc— in  the  cen- 
tral line  of  this  latter,  directly  under  the 
primitive  groove  or  medullary  furrow,  ap- 
pears the  simple  chorda  dorsalis.    (Cf.  Figs. 
84-87,   vol.  i.  pp.  297,  298,  surface   view; 
Figs.  66-70,  89-93,  transverse  section;  also 
Plates  IV.,  V,  ch.)    As  a  cylindrical  chord  it 
traverses  the  longitudinal  axis  of  the  body, 
and  is  equally  pointed  at  both  ends.     The 
cells  which  compose  the  chord  (Fig.  257,  b) 
come,  in  common  with  all  the  other  cells  of 
the  skeleton,   from  the  skin-fibrous    layer. 
They  most  resemble  certain  cartilage  cells ; 
a  special  "  chordal  tissue  "  is  often  said  to 
exist;   but  this  must  not  be  regarded   as 
more   than  a   special  form  of  cartilaginous  tissue.     At  an 
early  period  the  notochord  envelopes  itself  in  a  structureless 
sheath  (a)  as  clear  as  glass,  which  is  secreted  by  its  cells. 


Fig.  257.— Por- 
tion of  notochord 
(chorda  dorsalis)  of 
an  embryo  sheep  : 
a,  sheath  ;  b,  cells. 
(After  Koelliker.) 


DEVELOPMENT  OF  TUE  VERTEBRAL  COLUMN.     287 

This  perfectly  simple,  inarticulate,  primary  axial 
skeleton  is  soon  replaced  by  an  articulated,  secondary 
axial  skeleton,  called  the  "  vertebral  column."  On  each  side 
of  the  notochord  the  primitive  vertebral  bands  or  primitive 
vertebral  plates  (vol.  i.  p.  30G,  Fig.  92,  utv)  differentiate  from 
the  inner  portion  of  the  skin-fibrous  layer.  The  inner  part 
of  these  primitive  vertebral  bands,  which  immediately  sur- 
rounds the  notochord,  is  the  skeleton-plate,  or  skeleton 
stratum  (i.e.,  the  cell-layer  forming  the  skeleton),  which 
furnishes  the  tissue  for  the  rudiments  of  the  permanent 
vertebral  column  and  of  the  skull.  In  the  anterior  half 
of  the  body  the  primitive  vertebral  plate  remains  a  simple, 
continuous,  unbroken  layer  of  tissue,  and  soon  expands  into 
a  thin- walled  vesicle,  which  surrounds  the  brain  ;  this  is  the 
primordial  skull.  In  the  posterior  half,  on  the  contrary, 
the  primitive  vertebral  plate  breaks  up  into  a  number  of 
homologous  cube-shaped  pieces,  lying  one  behind  the  other, 
these  are  the  several  primitive  vertebrad.  The  number 
of  these  is  at  first  very  small,  but  soon  increases,  as  the 
germ  grows  in  the  posterior  direction  (Figs.  258-2G0,  uiv). 
The  first  and  earliest  primitive  vertebrae  are  the  foremost 
neck-vertebra) ;  the  posterior  neck-vertebras  then  originate ; 
then  the  anterior  breast-vertebra?,  etc.  The  lowest  of  the 
tail-vertebrae  arise  last.  This  successive  ontogenetic  growth 
of  the  vertebral  column  in  a  direction  from  front  to  rear 
may  be  explained  phylogenetically  by  regarding  the  many- 
membered  vertebrate  body  as  a  secondary  product,  which 
has  originated  from  an  originally  inarticulate  parent-form 
by  progressive  metameric  development,  or  articulation. 
Just  as  the  many-membered  Worms  (Earth-worm,  Leech) 
and  the  closely  allied  Arthropods  (Crabs,  Insects)  originally 


288 


THE   EVOLUTION   OF   MAN. 


WW'  i  ! 


'\'^m 


— — v 


■±-m 

I — .f 

1 —  & 

J — » 

^  —  Zv 
'is. 


S3  j  ,P  ! 


*"/• 


■■/ 


Figs.  258-260. — Lyre-shaped  germ-shield  of  a  Chick,  in  three  consecutive 
stages  of  development ;  seen  from  the  dorsal  side ;  enlarged  about  twenty 
times.  Fig.  258,  with  six  pairs  of  primitive  vertebrae.  The  brain  is  a  sim- 
ple bladder  (Jib).  The  spinal  furrow  from  x  remains  wide  open  ;  behind,  at 
z,  it  is  much  enlarged.  tnp,  Marrow-plates;  sp,  side-plates;  y,  limit  be- 
tween the  pharynx  cavity  (sh)  and  the  head-intestine  {yd).  Fig.  259,  with 
ten  pairs  of  primitive  vertebra?.  The  brain  has  separated  into  three 
bladders  :  v,  fore-brain  ;  m,  mid-brain  ;  h,  hind-brain ;  c,  heart ;  dv,  yelk- 
veins.  The  spinal  furrow  is  still  wide  open  (z).  mp,  Marrow-plates. 
Fig.  260,  with  sixteen  pairs  of  primitive  vertebrae.    The  brain  has  separated 


PKIMITIVE   VERTEBRAE.  289 

into  five  bladders:  v,  fore-brain;  z,  twixt-brain ;  m,  mid-brain;  h,  hind- 
brain;  n,  after-brain;  a,  eye-vesicles ;  g,  ear-vesicles ;  c,  heart;  dv,  yelk- 
veins  ;  mp,  marrow-plate  ;  uiv,  primitive  vertebra. 

developed  from  an  inarticulate  worm-form  by  terminal 
budding,  so  the  many-membered  vertebrate  body  has 
originated  from  an  inarticulate  parent-form.  The  nearest 
extant  allies  of  this  parent-form  are  the  Appendicularia 
(Fig.  162)  and  the  Ascidian  (Plate  XI.  Fig.  14). 

As  has    been    repeatedly   pointed    out,   this   primitive 
vertebral,   or   metameric   structure   has   a   very  important 
bearing  on  the  higher  morphological  and  physiological  de- 
velopment of  Vertebrates.    (Cf.  vol.  i.  p.  34G.)    For  the  articu- 
lation is  by  no  means  confined  to  the  vertebral  column,  but 
ecmally  affects  the  muscular,  nervous,  vascular,  and  other 
systems.     As  is  shown  by  the  Amphioxus,  the  metameric 
structure  appeared  much    earlier  in  the  muscular  than  in 
the  skeleton  system.     Each  so-called  primitive  vertebra  is 
in  fact  far  more  than  the  mere  rudiment  of  a  future  verte- 
bra.    In  each  primitive  vertebra  exists  the  rudiment  of  a 
segment  of  the  dorsal  muscles,  of  a  pair  of  spinal  nerve- 
roots,  etc.     Only  the  inner  portion — that  which  lies  directly 
next  to  the  notochord  and  the  medullary  tube— is  employed, 
as  the  skeleton-plate,  in  the  formation  of  actual  vertebrce. 
We  have  already  seen  how  these  true  vertebrse  develop  from 
the  skeleton-plate  of  the  primitive  vertebras  or  metamera. 
The  right  and  left  lateral  halves  of  each  primitive  vertebra, 
originally  separate,  unite.    The  ventral  edges,  meeting  below 
the  medullary  tube,  surround  the  chord  and  thus  form  the 
rudiments  of  the  vertebral  bodies  ;  the  dorsal  edges,  meeting 
above  the  medullary  tube,  form  the  first  rudiments  of  the 
vertebral  arches.    (Cf.  Figs.  95-98,  and  Plate  IV.  Figs.  3-8.) 


290 


THE   EVOLUTION   OF   MAN. 


In  all  Skulled  Animals  (Craniota),  most  of  the  soft, 
undifferentiated  cells  which  originally  constitute  the 
skeleton-plate,  afterwards  change  into  cartilage  cells,  which 
secrete  a  firm,  elastic  "intercellular  sub- 
stance," and  thus  produce  cartilaginous 
tissue.  Like  most  other  parts  of  the 
skeleton,  the  rudimentary  vertebras  soon 
pass  into  a  cartilaginous  condition,  and, 
in  the  higher  Vertebrates,  the  cartila- 
ginous tissue  is  afterwards  replaced  by 
the  rigid  bony  tissue  with  its  peculiar 
radiate  bone-cells  (Fig.  5,  vol.  i.  p.  12G). 
The  original  axis  of  the  vertebral  column, 
human  embryo  of  eight    the  notochord,  is  more  or  less  compressed 

weeks,  in  lateral  Ion-      -,        .,  i-i       •  .-  i  •   i 

by  the  cartilaginous  tissue  which  grows 
vigorously  round  it.  In  lower  Verte- 
brates (i.e.,  in  Primitive  Fishes)  a  more 
or  less  considerable  portion  of  the  noto- 
chord remains  within  the  vertebral 
bodies.  In  Mammals,  on  the  contrary,  it  disappears  almost 
entirely.  In  the  human  embryo,  even  at  the  end  of  the 
second  month,  the  notochord  is  seen  only  as  a  thin  thread 
which  passes  through  the  axis  of  the  thick  cartilaginous  ver- 
tebral column  (Fig.  261,  ch).  In  the  cartilaginous  vertebral 
bodies  themselves,  which  afterwards  ossify,  the  thin  remnant 
of  the  notochord  (Fig.  262,  ch)  soon  disappears  entirely.  A 
remnant  remains,  however,  throughout  life  in  the  elastic 
"  intervertebral  discs "  which  develop,  from  the  skeleton 
plate,  between  each  pair  of  vertebral  bodies  (Fig.  261,  li). 
In  a  new-born  child,  a  large,  pear-shaped  cavity,  filled  with 
a  gelatinous  cell-mass,  is  visible  in  each  intervertebral  disc 


Fig.     261.— Three 
breast-vertebrte   of    a 


gitudinal  section  :  v, 
cartilaginous  vertebral 
bodies ;  li,  interverte- 
bral discs  ;  ch,  noto- 
chord. (After  Koel- 
liker.) 


EVOLUTION  OF  THE  NOTOCHORD.         29 1 

(Fig.  203,  a).  This  "  gelatinous  nucleus"  of  the  elastic  ver- 
tebral disc  becomes  less  sharply  defined,  but  persists 
throughout  life  in  all  Mammals,  while  in  Birds  and  Rep- 
tiles,  even   the   last   remnant   of  the   notochord   vanishes. 


Fig.  262. — A  breast-vertebra  of  the  same  embryo  in  lateral  cross-section: 
cv,  cartilaginous  vertebral  bodies ;  ch,  notochord ;  pr,  square  process ; 
a,  vertebral  arch  (upper)  ;  c,  upper  end  of  rib  (lower  arch).  (After 
Koelliker.) 

Fig.  263. — Intervertebral  disc  of  new-born  child  in  cross-section : 
a,  remnant  of  the  notochord.     (After  Koelliker.) 

When  the  cartilaginous  vertebras  afterwards  ossify,  the  first 
deposit  of  bone-substance  (the  first  "bone-nucleus")  in 
the  vertebral  bodies  is  formed  immediately  round  the  rem- 
nant of  the  notochord,  and  soon  completely  displaces  the 
latter.  A  special  bone  kernel  or  nucleus  is  then  formed  in 
each  half  of  the  cartilaginous  vertebral  arch.  It  is  not  till 
after  birth  that  the  ossification  progresses  so  far  that  the 
three  bone-nuclei  approach  each  other.  The  two  bony 
halves  of  the  arch  unite  during  the  first  year,  but  it  is  not 
till  much  later,  till  between  the  eighth  and  the  twelfth 
year,  that  they  unite  with  the  bony  vertebral  body. 

The  bony  skull  (cranhim),  which  must  be  regarded  as 


292 


THE   EVOLUTION   OF   MAN. 


the  foremost,  peculiarly  modified  section  of  the  vertebral 
column,  develops  in  an  exactly  similar  manner.  Just  as, 
in  the  spinal  column,  the  vertebral  canal  envelopes  and  pro- 
tects the  dorsal  marrow,  so  the  skull  forms  a  bony  covering 
round  the  brain;  and,  as  the  brain  is  merely  the  anterior, 
peculiarly  differentiated  portion  of  the  dorsal  marrow,  we 
might  conclude  on  a  'priori  grounds,  that  the  bony  envelope 
of  the  brain  is  a  peculiar  modification  of  that  of  the  dorsal 
marrow.  It  is  true,  that  if  the  developed  human  skull 
(Fig.  264)  is  considered  by  itself,  it  is  impossible  to  under- 
stand how  it  can  be  merely  the  modified  anterior  portion  of 
the  vertebral  column.  It  is  a  complex,  capacious  bony 
structure,  consisting  of  no  less  than  twenty  bones,  differing 

widely  in  form  and  size.  Seven  of 
these  skull-bones  constitute  the 
spacious  case  which  encloses  the 
brain,  and  in  which  we  distinguish 
the  strong,  massive  floor  of  the  skull 
(basis  cranii)  below,  and  the 
boldly  arched  roof  of  the  skull 
Fig.  264-Human  skull,  (fornix  cranii)  above.  The  other 
from  the  right  side.  thirteen    bones    form    the    "  facial 

skull,"  which  especially  provides  the  bony  envelopes  of 
the  higher  sense-organs,  and  at  the  same  time  as  the  jaw- 
skeleton,  encircles  the  entrance  to  the  intestinal  canal. 
The  lower  jaw  (usually  regarded  as  the  twenty-first 
skull-bone)  is  jointed  to  the  skull-floor,  and  behind  this, 
embedded  in  the  roots  of  the  tongue,  we  find  the  tongue- 
bone,  which,  like  the  lower  jaw,  has  originated  from  the 
gill-arches,  together  with  a  portion  of  the  lower  arch,  which 
originally  developed  as  "  skull-ribs  "  from  the  ventral  side 
of  the  skull-floor. 


VERTEBRAL   THEORY   OF   THE   SKULL.  293 

Although,  therefore,  the  developed  skull  of  the  higher 
Vertebrates,  in  its  peculiar  form,  its  very  considerable  size, 
and  its  complex  structure,  seems  to  have  nothing  in 
common  with  ordinary  vertebrae,  yet  the  old  comparative 
anatomists  at  the  close  of  the  eighteenth  century  correctly 
believed  that  the  skull  is  originally  merely  a  series  of 
modified  vertebrae.  In  1790,  Goethe  "  picked  up  out  of  the 
sand  of  the  Jews'  burying-ground  among  the  downs  near 
Venice,  a  dismembered  skull  of  a  sheep ;  he  at  once  per- 
ceived that  the  face  bones  (like  the  three  vertebrae  of  the 
back  of  the  skull)  are  also  derivable  from  vertebras."  And, 
in  1S06,  Oken  (without  knowing  of  Goethe's  discovery),  at 
Ilsenstein,  on  the  way  to  the  Brocken,  "  found  a  beautifully 
bleached  skull  of  a  hind;  the  thought  flashed  through  him, 
It  is  a  vertebral  column  ! "  179 

For  the  last  seventy  years,  this  celebrated  "  Vertebral 
Theory  of  the  Skull  "  has  interested  the  most  prominent 
zoologists ;  the  most  important  representatives  of  Compara- 
tive Anatomy  have  exercised  their  ingenuity  in  attempting 
to  solve  this  philosophical  skull-problem  ;  and  the  question 
has  engaged  attention  in  yet  wider  circles.  It  was  not  till 
1S72  that  the  solution  was  found,  after  seven  years  of 
labour,  by  the  comparative  anatomist,  who,  both  in  the 
wealth  of  his  real  empirical  knowledge  and  in  the  pro- 
fundity of  his  philosophic  speculations,  surpasses  all  other 
students  of  this  science.  Karl  Gegenbaur,  in  his  classic 
"Researches  in  the  Comparative  Anatomy  of  Vertebrates" 
(third  part),  showed  that  the  skull  skeleton  of  the  Selachii 
is  the  only  record  which  affords  definite  proof  of  the  verte- 
bral theory  of  the  skull.  Earlier  comparative  anatomists 
erred  in  starting  from  the  developed  mammalian  skull,  and 


294  THE   EVOLUTION   OF  MAN. 

in  comparing  the  several  component  bones  with  the  separate 
parts  of  vertebras  ;  they  supposed  that  in  this  way  they 
could  prove  that  the  developed  mammalian  skull  consists 
of  from  three  to  six  original  vertebrae  The  hindmost  of 
these  skull-vertebrae  was,  according  to  them,  the  occipital 
bone.  A  second  and  a  third  vertebra  were  represented  by 
the  sphenoid  bone,  with  the  parietal  bones,  and  by  the 
frontal  bone,  etc.  The  elements  of  anterior  skull  vertebrae 
were  even  supposed  to  exist  in  the  face  bones.  In  opposi- 
tion to  this  view,  Huxley  first  called  attention  to  the  fact 
that  in  the  embryo  this  bony  skull  originally  develops 
from  a  simple  cartilaginous  vesicle,  and  that  in  this  simple 
cartilaginous  "  primitive  skull "  not  the  slightest  trace  of  a 
constitution  of  vertebrate  parts  is  visible.  This  is  equally 
true  of  the  skulls  of  the  lowest  and  most  ancient  Skulled 
Animals  (Craniota),  the  Cyclostomi  and  the  Selachii.  In 
these  the  skull  retains  throughout  life  the  form  of  a  simple 
cartilaginous  capsule — of  an  inarticulate  "  primitive  or 
primordial  skull."  If  the  older  skull-theoiy,  as  it  was 
accepted  from  Goethe  and  Oken  by  most  comparative 
anatomists,  were  correct,  then  in  these  ■  lowest  Skulled 
Animals  especially,  and  in  the  embryos  of  the  higher  Skulled 
Animals,  the  constitution  of  the  "  primitive  skull "  by  a 
series  of  "  skull-vertebra?  "  would  be  very  clearly  evident. 

This  simple  and  obvious  consideration,  first  duly  em- 
phasized by  Huxley,  indeed  overturns  the  famous  "  Verte- 
brate Theory  of  the  Skull,"  as  held  by  the  older  comparative 
anatomists.  Yet  the  entirely  correct  fundamental  idea 
holds  good,  i.e.,  the  hypothesis  that  the  skull  develops  from 
the  anterior  portion  of  the  spinal  column  by  differentiation 
and  peculiar  modification,  just  as  the  brain  develops  from 


HUXLEY'S   SKULL   THEORY.  295 

the  anterior  portion  of  the  dorsal  marrow.  But  the  true 
mode  of  empirically  establishing  this  philosophic  hypothesis 
was  yet  to  be  discovered ;  and  this  discovery  we  owe  to 
Gegenbaur.180  He  was  the  first  to  employ  the  phylogenetic 
method,  which,  in  this  as  in  all  morphological  questions, 
leads  most  surely  and  quickly  to  the  result.  He  showed 
that  the  Primitive  Fishes  (Selachii,  Figs.  191,  192,  p.  113), 
as  the  parent-forms  of  all  Amphirhina,  yet  retain  per- 
manently in  their  skull-structure  that  form  of  primordial 
skull,  from  which  the  modified  skull  of  the  higher  Verte- 
brates, and  therefore  that  of  Man,  has  developed  phylo- 
genetically.  He  also  pointed  out  that  the  gill-arches  of  the 
Selachii  show  that  their  primordial  skull  was  originally 
formed  of  a  considerable  number — at  least  nine  or  ten — 
primitive  vertebrae,  and  that  the  brain-nerves,  which  branch 
from  the  base  of  the  brain,  entirely  confirm  this.  These 
brain-nerves — with  the  exception  of  the  first  and  the  second 
pairs  (the  olfactory  and  the  optic  nerves) — are  merely  modi- 
fied spinal  nerves,  and,  in  their  peripheric  distribution, 
essentially  resemble  the  latter.  The  Comparative  Anatomy 
of  these  brain-nerves  is  one  of  the  strongest  arguments  for 
the  newer  vertebral  theory  of  the  skull. 

It  would  lead  us  too  far  aside  if  we  were  to  enter  into 
the  particulars  of  this  ingenious  theory  of  Gegenbaur,  and 
I  must  content  myself  with  referring  to  the  great  work 
already  quoted  ;  in  it  the  theory  is  fully  demonstrated  by 
empirical  and  philosophical  arguments.  The  same  author 
has  given  a  brief  abstract  in  his  "  Outlines  of  Comparative 
Anatomy  "  (1874),  the  study  of  which  it  is  impossible  to 
recommend  too  highly.  In  this  work  Gegenbaur  indi- 
cates as  original  " skull-ribs,"  or  "lower  arches  of  skull- 
36 


296  THE  EVOLUTION   OF  MAN. 

vertebrae,"  in  the  selachian  skull  (Fig.  265),  the  following 
2?airs  of  arches :  I.  and  II.  are  two  lip  cartilages,  of  which 
the  anterior  (a)  consists  only  of  an  upper,  and  the  inferior 
(be)  of  an  upper  and  a  lower  piece ;  III.,  the  jaw-arch, 
which  also  consists  of  two  pieces  on  each  side, — viz.,  the 
primitive   upper   jaw   (os   rpalato-quadratum,   o)   and   the 


Fig.  265. — Head  skeleton  of  a  Primitive  Fish:  n,  nose-groove;  eth,  region 
of  the  sieve-bone  ;  orb,  eye-cavity  ;  la,  wall  of  ear-labyrinth  ;  occ,  occipital 
region  of  the  primitive  skull ;  cv,  vertebral  column ;  a,  front ;  be,  hind  lip- 
cartilage  ;  0,  primitive  upper  jaw  (palato  quadratuvi) ;  u,  primitive  lower 
jaw  ;  II.,  tongue-arch  ;  III. -VIII.,  first  to  sixth  gill-arches.  (After  Gegen- 
baur.) 

primitive  lower  jaw  («);  IV.,  the  tongue  arch  (II.),  and  V.  to 
X.,  six  true  gill  arches,  in  the  stricter  sense  of  that  term 
(III.-YIII.).  The  anatomical  features  of  these  nine  or  ten 
skull-ribs,  or  "  lower  vertebral  arches,"  and  of  the  brain 
nerves  distributed  over  them,  show  that  the  apparently 
simple,  cartilaginous  "  primordial  skull  "  of  the  Primitive 
Fishes  originally  develops  from  an  equal  number  (nine  at 
the  least)  of  primitive  vertebrae.  The  base  of  the  skull  is 
formed  by  the  vertebral  bodies  ;  the  roof  of  the  skull  by  the 
upper  vertebral  arches.  The  coalescence  and  amalgamation 
of  these  into  a  single  capsule  is,  however,  so  ancient,  that 


EVOLUTION  OF  THE  SKULL.  297 

their  primordial  separate  condition  now  appears  effaced  by 
the  action  of  the  "law  of  abridged  heredity,"  and  is  no 
longer  demonstrable  in  the  Ontogeny. 

In  the  human  primitive  skull  (Fig.  266),  and  in  that  of 
all  higher  Vertebrates,  which  has  been  modified,  phyloge- 
netically,  from  the  primitive  skull  of  the  Selachii,  five  con- 
secutive divisions  are  visible  at  a  certain  early  period  of 
development ;  these  one  might  be  tempted  to  refer  to  five 

Fig.  266. — Primitive  skull  of   human        .  , 

h 
embryo  of  four  weeks;  vertical  section,  n       I .  Y1 

the  left  half  seen  from  the  inside  :    v,  z,  -  "■ 

m,    h,  n,   the    five    grooves    in   the    skull     ~T  ''    ',         v  •  ',  -  ' 

.        .  v  '        ■ 

cavity,  in  which  lie  the  five  braiu -bladders        '  0  .   •       >    -    ji 

(fore-brain,  twixt-brain,  mid-brain,  hind-  <?*■   in        ', 

brain,    after-brain);    0,   pear-shaped    pri-  /^\l^     a 

mary  ear- vesicle  ;  a,  eye  ;  no,  optic  nerve  ; 

p,   canal   of   the   hypophysist;    t,  central  n  0  W  ,       WBt'  -/■ 

part  of  the  cranial  basis.  (After  Koelliker.)  \!||l!»^ 

original  primitive  vertebrae ;  they  are,  however,  merely  the 
result  of  adaptation  to  the  five  primitive  brain-bladders, 
and,  like  the  latter,  they  rather  correspond  to  a  larger 
11  umber  of  metarnera.  The  fact  that  the  primitive  verte- 
brate skull  is  a  much  modified  and  profoundly  transformed 
organ,  and  by  no  means  a  primitive  structure,  is  also  evi- 
dent in  the  circumstance  that  its  rudiment,  originally  a  soft 
membrane,  commonly  assumes  the  cartilaginous  state  only 
at  its  base  and  on  the  sides,  while  it  remains  membranous 
at  the  skull-roof.  Here  the  bones  of  the  later  bony  skull 
develop  in  the  soft  membranous  rudiment  as  an  external 
bony  roof,  without  a  previous  intermediate  cartilaginous 
Btate,  as  in  the  base  of  the  skull.  Thus  a  great  part  of  the 
skull-bones    originally    developed    as   roof- bones   from    the 


298  THE  EVOLUTION   OF  MAN. 

leather-skin  (corium),  and  only  secondarily,  come  into  closer 
relations  with  the  skull.  How,  in  Man,  this  most  simple  and 
•  primordial  rudiment  of  the  primitive  skull  develops,  onto- 
genetically,  from  the  head-plates,  and  how,  in  the  mean- 
time, the  anterior  extremity  of  the  notochord  is  enclosed  in 
the  base  of  the  skull,  has  already  been  explained.  (Cf. 
vol.  i.  p.  378 ;  Figs.  145  and  146,  p.  393.) 

The  main  features  in  the  history  of  the  development  of. 
the  gill-arches,  which  must  now  be  regarded  as  skull-ribs, 
has  been  told.  Of  the  four  original  rudimentary  gill-arches  of 
Mammals  (Plates  I.  and  VII,  Figs.  232-236,  p.  243),  the  first 
lies  between  the  primitive  mouth-opening  and  the  first  gili- 
opening.  From  the  base  of  this  gill-arch  the  "  upper  jaw 
process  "  develops,  and  this  unites,  in  the  manner  already 
described,  with  the  internal  and  the  external  nasal  processes 
on  each  side,  and  forms  the  chief  parts  of  the  upper  jaw  skele- 
ton palate-bones,  wing-bones,  etc.  (Cf.  p.  245  and  268.)  The 
rest  of  the  first  gill-arch,  now  distinguished  as  the  "  lower-jaw 
process,"  forms  out  of  its  base  two  ear  bonelets — the  hammer 
(malleus)  and  the  anvil  (incus);  the  rest  of  its  mass  becomes 
a  long  strip  of  cartilage,  called,  after  its  discoverer,  "  Meckel's 
cartilage."  On  the  external  surface  of  this  cartilage  origin- 
ates, as  a  surface-bone  (formed  of  cellular  matter  from  the 
leather-plate),  the  permanent  bony  lower  jaw.  From  the 
base  of  the  second  gill-arch  in  Mammalia  originate  the 
third  ear  bonelet,  the  stirrup  (stapes),  and  from  the  subse- 
quent parts,  in  order,  the  stirrup-muscle,  the  styloid  process  of 
the  temporal  bone,  the  styloid  band,  and  the  small  horn  of  the 
tongue-bone.  Finally,  the  third  gill-arch  becomes  cartilagin- 
ous only  at  its  anterior  portion,  and  here,  by  the  union  of  its 
two  halves,  is  formed  the  body  of  the  tongue-bone  (copula 


EVOLUTION  OF  THE  SKULL.  299 

hyoklea)  and  its  great  horn  on  each  side.  The  fourth  gill- 
arch  appears  in  the  mammalian  embryo  only  as  a  transient, 
rudimentary  embryonic  organ,  and  does  not  develop  into 
special  parts.  Of  the  posterior  gill-arches  (the  fifth  and 
sixth  pairs),  which  are  permanent  in  the  Primitive  Fishes,  no 
trace  is  visible  in  the  embryo  of  higher  Vertebrates.  The 
latter  have  long  been  lost.  The  four  gill-openings  in  the 
human  embryo  are  also  only  interesting  as  transient  rudi- 
mentary organs,  which  soon  disappear  entirely  by  concre- 
scence. The  first  gill-opening  (between  the  first  and  second 
gill-arches)  alone  is  of  permanent  importance ;  from  it 
develops  the  drum,  or  tympanic  cavity  of  the  ear,  and  the 
Eustachian  tube.  (Cf.  p.  269,  and  Plate  I.,  with  explan- 
ation.) 

Not  only  did  Gegenbaur,  in  his  model  "  Researches  into 
the  Comparative  Anatomy  of  Vertebrates,"  first  correctly 
explain  the  skull  and  its  relation  to  the  vertebral  column, 
but  he  also  first  performed  the  no  less  weighty  and  interest- 
ing task  of  showing  the  phylogenetic  derivation  of  the 
skeleton  of  the  limbs  in  all  Vertebrates  from  one  primordial 
form.  Few  parts  of  the  body  in  the  different  Vertebrates 
are  subjected,  by  adaptation  to  various  circumstances,  to 
such  an  infinite  variety  of  modifications  as  the  limbs,  in 
point  of  size,  form,  and  special  fitness  for  certain  purposes,  and 
yet  we  are  now  able  to  refer  them  all  to  one  common  here- 
ditary form.  Vertebrates  are  distinguishable  as  regards  the 
structure  of  their  limbs  into  three  large  main  groups.  The 
lowest  and  most  ancient  Vertebrates,  the  skull-less  and  jaw- 
less  classes,  like  all  their  invertebrate  ancestors,  had  no 
paired  limbs ;  this  condition  is  yet  represented  in  the  Am- 
phioxus  and  in  the  Cyclostomi  (Figs.  189,  190).     The  second 


300  THE   EVOLUTION   OF   MAN. 

main  group  consists  of  the  two  classes  of  true  Fishes,  and  of 
the  Dipneusta ;  in  these,  two  pairs  of  lateral  limbs,  in  the 
shape  of  many-fingered  swimming-fins — one  pair  of  pectoral 
fins  (the  fore  legs)  and  one  pair  of  abdominal  fins  (hind  legs) — 
are  originally  always  present  (Figs.  191,  192,  Plate  XII.). 
Finally,  the  third  main  group  embraces  the  four  higher 
vertebrate  classes :  Amphibia,  Reptiles,  Birds,  and  Mammals ; 
in  these  the  same  two  pairs  of  legs  exist  originally,  but  in 
the  form  of  five-fingered  feet.  The  digits  or  fingers  are 
often  fewer  than  five ;  sometimes,  also,  the  feet  are  quite 
aborted.  But  the  original  parent-form  of  the  entire  group 
had  anteriorly  and  posteriorly  five  digits  (Pentadactylism, 
p.  123). 

As  regards  the  Phylogeny  of  the  limbs,  from  their 
Comparative  Anatomy  it  appears,  therefore,  that  the  extre- 
mities originated  in  the  Fishes,  in  the  Primitive  Fishes 
(Selachii),  and  were  transmitted  from  these  to  all  higher 
Vertebrates  (all  the  Amphirhina),  first  in  the  form  of 
many-fingered  fins,  and  afterwards  as  five-fingered  feet 
(Figs.  267-272).  The  anterior  extremity — the  pectoral  fin 
(or  the  fore  leg) — is  originally  shaped  precisely  like  the 
posterior  extremity — the  ventral  fin  (or  the  hind  leg).  In 
the  one,  as  in  the  other,  the  true  limb,  externally  promi- 
nent, is  distinguishable  from  the  internal,  concealed  girdle, 
by  which  the  limb  is  attached  to  the  spinal  column — the 
shoulder-girdle  above,  the  pelvic  girdle  below. 

The  genuine  primitive  form  of  the  paired  limbs,  as  it 
existed  in  the  most  ancient  of  the  Primitive  Fishes  during 
the  Silurian  Period,  occurs  to  this  day  in  perfect  preserva- 
tion in  the  ancient  Ceratodus,  and  very  curious  Mud-fish  of 
Australia  (p.  119,  Plate  XII.).    In  this,  both  the  pectoral  and 


THE   LIMBS.  301 

the  ventral  fin  is  a  flat,  oval  paddle,  in  which  we  find  a 
feathered  or  biserial  cartilaginous  skeleton  (Fig.  267). 
This  skeleton  consists  firstly  of  a  strong,  articulated  fin-rod 
or  "  stem  "  (Fig.  267,  A  B),  which  extends  from  the  base  to 
the  tip  of  the  fin,  and  secondly,  of  a  double  row  of  thin, 
feathered  rays  (rr),  which  are  attached  to  both  sides  of  the 
central  rod,  like  the  pinnae  of  a  pinnate  leaf.  This  primi- 
tive fin,  first  recognized  by  Gegenbaur,  and  by  him  called 
the  Arch  i pterygium,  is  attached  to  the  spinal  column  by 
means  of  a  simple  girdle  in  the  shape  of  a  cartilaginous 
arch.181 

In  some  Sharks  and  Rays,  especially  when  very  young, 
this  same  primitive  fin  also  occurs  in  a  more  or  less  modified 
form.  But  in  most  Primitive  Fishes  the  fin  is  already 
essentially  modified,  in  that  the  rays  on  one  side  of  the  stem 
are  partly  or  altogether  lost,  and  are  retained  only  on  the 
other  side  (Fig.  268).  Hence  arises  the  half-feathered,  or 
uniserial  fish-fin,  inherited  by  the  other  fishes  from  the 
Selachii  (Fig.  269). 

Gegenbaur  first  showed  how  the  five-fingered  leg  of 
Amphibia  is  developed  from  this  uniserial  fin  (Fig.  270)  and 
is  inherited  by  three  classes  of  Amniota.  In  those  Dip- 
neusta  which  were  the  ancestors  of  the  Amphibia,  the  fin  rays 
on  the  other  side  of  the  stem  also  were  gradually  degraded 
in  development,  and  were  in  a  great  measure  lost  (the  light- 
coloured  cartilages  in  Fig.  269).  Only  the  four  lowest  rays 
(shaded  in  Fig.  269)  were  retained ;  and  these  are  the  four 
outer  digits  of  the  foot  (second  to  fifth  digits).  The  first, 
or  great  digit  (toe),  on  the  contrary,  originated  from  the 
Lower  part  of  the  fin-rod.  From  the  middle  and  upper  parts 
of  this  fin-rod  developed  the  long  main  stem  of  the  limbs 


302 


THE   EVOLUTION   OF   MAN. 


Fig.  267. 


Fig.  269. 


Fig.  270. 


Fig.  271. 


Fig.  272. 


EVOLUTION   OF   THE   LIMBS.  303 

Fig.  267. — Bones  of  pectoral  fins  of  Ceratodus  (Archipterygiuni,  or 
bilateral  pinnate  skeleton)  :  A  B,  series  of  cartilaginous  pieces  forming  the 
ventral  stem  of  the  fin ;  rr,  rays  of  the  fin.     (After  Giinther.) 

Fig.  268. — Bones  of  pectoral  fin  of  an  earlier  Primitive  Fish  (Acanthias) . 
Most  of  the  rays  of  the  medial  edge  of  the  fin  (B)  have  disappeared ;  only 
a  few  (R')  remain.  R  R,  rays  of  the  lateral  edge  of  fin ;  mt,  Metap- 
terygium  ;  ms,  Mezopterygium ;  p,  Propterygium.     (After  Gegenbaur.) 

Fig.  269. — Bones  of  pectoral  fin  of  a  more  recent  Primitive  Fish,  or 
Selachian.  The  rays  of  the  medial  edge  of  the  fin  have  entirely  dis- 
appeared. The  shaded  part  on  the  right  is  that  portion  which  develops  into 
the  five-fingered  hand  of  higher  Vertebrates  (b,  the  three  basal  pieces  of 
the  fin ;  mt,  Metapterygium ;  rudiment  of  the  humerus ;  ms,  Mezoptery- 
gium ;  p,  Propterygium) .     (After  Gegenbaur.) 

Fig.  270. — Bones  of  the  fore-limb  of  an  Amphibian :  h,  upper  arm 
(humerus) ;  r,  u,  lower  arm  (r,  radius  ;  u,  ulna)  ;  r,  c,  i,  c,  u,  root-bones  of  the 
hand,  first  row  (r,  radial ;  t,  intermediate ;  c,  central ;  u,  ulnary) ;  1, 2,  3, 4,  5, 
root-bones  of  the  hand,  second  row.     (After  Gegenbaur.) 

Fig.  271. — Bones  of  hand  of  Gorilla.     (After  Huxley.) 

Fig.  272. — Bones  of  human  hand,  seen  from  the  back.    (After  H.  Meyer.) 


which  is  so  prominent  in  the  higher  Vertebrata  as  the  upper 
arm  (or  leg)  (Fig.  270,  r  and  u)  and  the  lower  arm  (or 
leg,  h). 

The  many-fingered  fish-fins  thus  gave  rise,  by  a  process 
of  gradual  reversion  and  differentiation,  to  the  five-fingered 
amphibian  foot,  which  occurs  first  in  the  Sozobranchia,  and 
which,  from  them,  has  been  transmitted  on  the  one  hand  to 
Reptiles,  and  to  Mammals,  up  to  Man,  on  the  other  (Fig.  272) 
Simultaneously  with  the  reduction  of  the  number  of  the  fin- 
rays  to  four,  a  further  differentiation  affected  the  fin-stem  or 
rod ;  it  became  transversely  divided  into  the  upper  and 
lower  arms  (or  legs),  and  a  modification  took  place  in 'the 
girdle,  which  in  the  higher  Mammals  originally  consists, 
both  anteriorly  and  posteriorly,  of  three  bones.  The  simple 
arch  of  the  original  shoulder-girdle  separates,  on  each  side 
into  an  upper  (dorsal)  piece — the  shoulder-blade  (scapula) 


304  THE   EVOLUTION    OF   MAN. 

and  a  lower  (ventral)  piece;  the  anterior  portion  of  the 
latter  constitutes  the  pro-key  (or  collar)  bone  (procoracoi- 
deum)  and  its  posterior  part  the  raven-bone  (coracoideum). 
The  simple  arch  of  the  pelvic  girdle  breaks  up,  correspond- 
ingly, into  an  upper  (dorsal)  piece — the  intestinal  bone 
(os  ilium),  and  a  lower  (ventral)  piece ;  the  anterior  portion 
of  the  latter  becomes  the  pubic  bone  (os  pubis)  and  the 
posterior  portion  the  hip-bone  (os  ischii).  Table  XXXIV., 
p.  278,  shows  the  correspondence  of  these  three  parts  of 
the  pelvic  girdle  with  those  of  the  shoulder-girdle.  The 
latter,  however,  in  the  key-bone  or  collar-bone  (clavicula), 
possesses  a  fourth,  wanting  in  the  former.  (Cf.  Gegenbaur.182) 
As  in  the  girdle,  so  in  the  trunk  of  the  limbs  there  is 
originally  an  absolute  agreement  between  the  anterior  and 
posterior  limbs.  The  first  section  of  the  trunk  is  supported 
by  a  single  strong  bone — in  the  anterior  limbs,  the  upper 
arm  (humerus) ;  in  the  posterior,  the  upper  leg  (femur). 
The  second  section,  on  the  other  hand,  contains  two  bones — 
on  the  anterior  extremity  the  spoke-bone  (radius,  Fig. 
270,  r),  and  the  ell-bone  (ulna,  Fig.  270,  u) ;  in  the  posterior 
the  two  corresponding  bones,  the  shin-bone  (tibia)  and 
calf-bone  (fibula).  (Cf.  skeletons  in  Fig.  196  and  Figs. 
204-208).  Moreover,  the  subsequent  small  and  numerous 
bones  of  the  wrist  (carpus)  and  of  the  ankle  (tarsus)  cor- 
respond ;  so  do  the  five  bones  of  the  middle  of  the  hand 
{metacarpus)  and  of  the  middle  of  the  foot  (metatarsus). 
Finally,  the  same  is  true  of  the  five  digits  attached  to  these 
parts,  which  in  their  characteristic  structure  of  a  series  of 
bone-pieces  correspond  in  the  anterior  and  posterior  limbs. 
Charles  Martins,  of  Montpellier,  an  excellent  morphologist 
has  shown  that,  in  detail,  the  anterior  and  posterior  limbs 
correspond.183 


HOMOLOGY   OF   THE   LIMBS.  305 

As  Comparative  Anatomy  thus  shows  that  the  skeleton 
of  the  limbs  in  Man  is  composed  of  the  same  bones,  and  in 
the  same  manner  as  the  skeleton  in  the  four  higher  verte- 
brate classes,  we  may  justly  infer  their  common  descent 
from  a  single  parent-form.  This  parent-form  was  the  most 
ancient  Amphibian  possessing  five  digits  both  on  the  fore 
and  on  the  hind  limbs.  The  outermost  part  of  the  limbs 
has,  indeed,  been  very  much  modified  by  adaptation  to 
various  conditions  of  life.  The  diversities  in  this  point 
within  the  mammalian  class  are  enormous.  The  slender 
limbs  of  the  swift  Deer  and  the  strong,  springy  legs  of  the 
Kangaroo,  the  climbing  feet  of  the  Sloth  and  the  digging- 
paws  of  the  Mole,  the  fins  of  the  Whale  and  the  wings  of 
the  Bat,  are  all  instances.  It  will,  of  course,  be  admitted  by 
all  that  these  organs  of  locomotion  are  as  diverse  as  possible 
in  point  of  size,  form,  and  special  function.  And  yet  the 
internal  bony  skeleton  is  substantially  the  same  in  them  all. 
In  all  these  different  forms  of  limbs  the  same  characteristic 
bones  are  always  represented  in  essentially  the  same  strongly 
inherited  combination ;  and  here  we  have  a  weighty  confirm- 
ation of  the  theory  of  descent,  such  as  is  hardly  afforded  by 
the  Comparative  Anatomy  of  any  other  organ.  (Cf.  Plate 
IV.  p.  34,  vol.  ii.  of  "  History  of  Creation.")  True,  in  the 
limbs  of  the  different  Mammals,  the  skeleton  is  subject  to 
various  arrests  of  development  and  reversions,  in  addition 
to  those  due  to  special  adaptation  (Fig.  273).  Thus,  in  the 
fore  foot  (or  hand)  of  the  Dog  the  first  digit,  or  thumb,  is 
aborted  (Fig.  273  II.).  In  the  Pig  (III.)  and  the  Tapir  (V.) 
this  digit  has  entirely  disappeared.  So,  too,  in  the  Rumi- 
nants (e.y.,  the  Ox,  Fig.  IV.)  the  second  and  fifth  digits  are 
also  aborted,  and  only  the  third  and  fourth  are  well  deve- 


306 


THE    EVOLUTION   OF   MAN. 


loped.  Finally,  in  the  Horse,  only  one  digit,  the  third,  is 
perfectly  developed  (Fig.  VI.,  3).  And  yet  all  these  diverse 
fore-feet,  as  also  the  hand  of  the  Ape  (Fig.  271)  and  the 
human  hand  (Fig.  272),  have  originated  from  the  same 
common  five-lingered  parent-form.  This  is  proved,  not  only 
by  the  rudiments  of  the  aborted  digits,  but  also  by  the 
homologous  disposition  of  the  wrist-bones  (Fig.  273,  a-p). 
{Vide  supra,  p.  124.) 

The  same  story  is  also  told  by  the  germ-history  of  the 
limbs,  which  is  originally  identical,  not  only  in  all  Mammals, 
but  in  all  Vertebrates.  However  different  the  limbs  of  the 
various  Skulled  Animals  (Craniota)  afterwards  appear  in 
their  fully  developed  state,  they  nevertheless  all  originate 
from  the  same  simple  rudiment.     (Cf.  Plates  VI.  and  VII., 


4   3 


Fig.  273. — Skeleton  of  hand  or  fore-foot  of  six  Mammals.  I.  Man;  II. 
Dog ;  III.  Pig ;  IV.  Ox ;  V.  Tapir ;  VI.  Horse,  r,  Eadius ;  u,  ulna ; 
o,  scaphoid ;  b,  semi-lunar ;  c,  triquetrum  (cuneiform) ;  d,  trapezium ;  e, 
trapezoid  ;  /,  capitatum  (unciform  process) ;  g,  hamatum  (unciform  bone) ; 
p,  pisiform;  1,  thumb;  2,  digit;  3,  middle  finger;  4,  ring  finger;  5,  little 
finger.     (After  Gegenbaur.) 


OKIGIN   OF   THE   LIMBS.  307 

vol.  i.  p.  362 ;  /,  fore-leg,  b,  hind-leg.)  In  all,  the  first  rudi- 
ment of  each  limb  in  the  embryo  is  a  simple  wart,  or  small 
knob,  which  grows  from  the  side  of  the  body  between  the 
dorsal  and  ventral  sides  (Figs.  119  and  120,  vol.  i.  pp.  357,  359 ; 
136  and  137,  pp.  381,  382).  The  cells  composing  these  knobs 
belong  to  the  skin-fibrous  layer.  The  outer  surface  is  coated 
b}7  the  horn-plate,  which  is  rather  thicker  at  the  apex  of 
the  protuberance  (Plate  IV.  Fig.  5,  x).  The  two  anterior 
protuberances  appear  at  a  rather  earlier  period  than  the 
two  posterior.  By  differentiation  of  the  cells,  these  simple 
rudiments  develop  immediately,  in  Fishes  and  in  the 
Dipneusta,  into  fins.  In  the  higher  vertebrate  classes,  on 
the  contrary,  each  of  the  four  protuberances,  in  the  course 
of  its  development,  assumes  the  form  of  a  stalked  plate,  the 
inner  portion  of  which  being  narrower  and  thicker,  the 
outer  broader  and  thinner.  The  inner  portion,  or  the  handle 
of  the  plate,  then  divides  into  two  sections :  the  upper  and 
lower  legs  (or  arms).  Four  notches  then  appear  in  the  free 
edge  of  the  plate,  and  these  gradually  become  deeper ;  these 
are  the  divisions  between  the  five  digits  (Plate  VIII.  Fig.  1). 
The  latter  soon  become  more  prominent.  At  first,  however, 
all  the  five  digits,  both  on  the  fore  and  on  the  hind  limbs, 
are  joined  by  a  thin  connecting  web-like  membrane;  this 
recalls  the  original  adaptation  of  the  foot  as  a  swimming-fin. 
The  further  development  of  the  limbs  from  this  most  simple 
rudiment  takes  place  in  the  same  way  in  all  Vertebrates ; 
that  is,  by  the  modification  of  certain  groups  of  the  cells  of 
the  skin-fibrous  layer  into  cartilage,  of  other  groups  into 
muscles,  yet  others  into  blood-vessels,  nerves,  etc.  Probably 
the  differentiation  of  all  these  various  tissues  occurs  actuallv 
in  the  limbs.     Like  the  vertebral  column  and  the  skull,  the 


3<d8  the  evolution  of  man. 

bony  parts  of  the  limbs  are  also  formed  at  first  from  soft 
undifferentiated  cell-groups  of  the  skin-fibrous  layer.  These 
afterwards  change  into  cartilage,  and  from  these  the  per- 
manent bones  originate  by  a  tertiary  process.184 

The  development  of  the  muscles,  or  the  active  organs  of 
locomotion,  is,  as  yet,  of  much  less  interest  than  that  of  the 
skeleton,  or  the  passive  instruments  of  motion.  The  Com- 
parative Anatomy  of  these  is,  indeed,  of  much  higher  im- 
portance than  their  Embryology.  But  as  very  little  attention 
has,  as  yet,  been  paid  to  the  Comparative  Anatomy  and 
Ontogeny  of  the  muscular  system,  we  have  only  very 
general  ideas  of  its  Phylogeny  also.  The  muscular  system 
as  a  whole  has  developed  in  the  most  intimate  reciprocal 
correlation  with  the  bone  system.185 


(     309    ) 


TABLE   XXXV. 

Systematic   Survey  of  the  most  Important  Periods  in  the  Phylogeny 
of  the  Human  Skeleton. 

I.  First  Period  :  Skeleton  of  the  Chordoma  (Fig.  187,  p.  90). 
The  entire  skeleton  is  formed  by  the  notochord. 

II.  Second  Period  .-   Skeleton  of  the  Acrania  (Fig.  189,  p.  91). 

A  notochord-membrane,  the  dorsal  continuation  of  which  forms  a  cover- 
ing round  the  medullary  tube,  is  formed  round  the  notochord. 

III.  Third  Period  .-  Skeleton  of  the  Cyclostomi  (Fig.  190,  p.  103). 

A  cartilaginous  primordial  skull  develops  round  the  anterior  extremity 
of  the  notochord,  from  the  notochord-membrane.  An  outer  cartilaginous 
gill-skeleton  forms  round  the  gills. 

IV.  Fourth  Period  :  Skeleton  of  the  older  Selachii  (Fig.  268,  p.  302). 
A  primitive   vertebral  column,   with   upper  and  lower  arches  (the  gill- 
arches  and  ribs)  forms  round  the  notochord.     The  remnant  of  the  outer  gill- 
skeleton  remains  with  the  inner.     Two  pairs  of  limbs,  with  pinnate  (biserial) 
skeletons,  appear. 

V.  Fifth  Period:  Skeleton  of  the  more  recent  Selachii  (Fig.  269,  p.  302). 

The  anterior  gill-arches  change  into  lip-cartilage  and  jaw-arches.  The 
external  gill-skeleton  is  lost.  The  skeleton  of  the  two  pairs  of  fins  becomes 
uniscrial  (semi-pinnate). 

VI.  Sixth  Period, :  Skeleton  of  the  Dipneusta  (Fig.  2,  Plate  XII.). 
The  skull  becomes  partially  ossified ;  as  does  tho  shoulder-girdle. 

VII.  Seventh  Period :  Skeleton  of  the  Amphibia  (Fig.  270,  p.  302). 

ill-arches  are  modified  into  parts  of  the  tongue-bone,  and  of  tho  jaw- 
apparatus.  On  the  semi-pinnate  skeletons  of  the  fins  the  rays  diminish  in 
number  to  four,  thus  giving  rise  to  the  five-toed  foot.  Tho  vertebral 
column  ossifies. 


3IO  THE    EVOLUTION    OF   MAN. 

VIII.  Eighth  Period:  Skeleton  of  the  Monotremata  (Fig.  196,  p.  148). 

The   vertebral   column,    skull,   jaws,    and    limbs,   acquire    the    definite 
characteristics  of  Mammals. 

IX.  Ninth  Period  :  Skeleton  of  the  Marsupialia  (Fig.  197,  p.  152). 

The   coracoid  bone  of   the  shoulder. girdle  becomes  atrophied,  and  the 
remnant  of  it  amalgamates  with  the  shoulder- blade. 

X.  Tenth  Period  :  Skeleton  of  the  Semi-apes  (Fig.  199,  p.  164). 

The    pouch-bones,    which    distinguish    Monotremes    and    Marsupials, 
disappear. 

XI.  Eleventh  Period  :  Skeleton  of  the  Anthropoid  Apes 
(Figs.  204-208,  p.  179). 

The   skeleton   acquires   the   peculiar   development   shared   by  Man  ex- 
clusively with  the  Anthropoid  Apes. 


CHAPTER  XXIII. 

DEVELOPMENT   OF   THE   INTESTINAL   SYSTEM. 

The  Primitive  Intestine  of  the  Gastrula. — Its  Homology,  or  Morphological 
Identity  in  all  Animals  (excepting  the  Protozoa). — Survey  of  the 
Structure  of  the  Developed  Intestinal  Canal  in  Man. — The  Mouth- 
cavity. — The  Throat  (pharynx). — The  Gullet  (cesophagus). — The  "Wind- 
pipe (trachea)  and  Lungs. — The  Larynx. — The  Stomach. — The  Small 
Intestine. — The  Liver  and  Gall-bladder. — The  Ventral  Salivary  Gland 
(pancreas). — The  Large  Intestine. — The  Kectum. — The  First  Rudiment  of 
the  Simple  Intestinal  Tube. — The  Gastrula  of  the  Amphioxus  and  of 
Mammals. — Separation  of  the  Germ  from  the  Intestinal  Germ  Vesicle 
(Gastrocystis). — The  Primitive  Intestine  (Protogaster)  and  the  After 
Intestine  (Metagaster). — Secondary  Formation  of  the  Mouth  and  Anus 
from  the  Outer  Skin. — Development  of  the  Intestinal  Epithelium  from 
the  Intestinal-glandular  Layer,  and  of  all  other  parts  of  the  Intestine 
from  the  Intestinal-fibrous  Layer. — Simple  Intestinal  Pouch  of  the 
Lower  Worms. — Differentiation  of  the  Primitive  Intestinal  Tube  into  a 
Respiratory  and  a  Digestive  Intestine. — Gill-intestine  and  Stomach- 
Intestine  of  the  Amphioxus  and  Ascidian. — Origin  and  Significance  of 
the  Gill-openings. — Their  Disappearance. — The  Gill-arches  and  the  Jaw- 
skeleton. — Formation  of  the  Teeth. — Development  of  the  Lungs  from  the 
Swim-bladder  of  Fish. — Differentiation  of  the  Stomach. — Development 
of  the  Liver  and  Pancreas. — Differentiation  of  the  Small  and  Large 
Intestines. — Formation  of  the  Cloaca. 

"  Cautious  people  require  us  to  confine  ourselves  to  gathering  materials, 
and  to  leave  it  to  posterity  to  raise  a  scientific  structure  from  those 
materials  ;  because  only  in  that  way  can  we  escape  the  ignomiuy  of  having 
the  theories  we  believed  in  overthrown  by  the  advance  of  knowledge.  The 
unreasonableness  of  this  demand  is  apparent   enough  from   the  fact  that 


312  THE   EVOLUTION    OF   MAN. 

Comparative  Anatomy,  like  every  other  science,  is  endless ;  and  therefore 
the  endlessness  of  the  accumulation  of  materials  would  never  allow  men,  if 
they  complied  with  this  demand,  to  reap  any  harvest  from  this  field.  But, 
further  than  this,  history  teaches  us  clearly,  that  no  age  in  which  scientific 
inquiry  has  been  active,  has  been  able  so  to  deny  itself,  as,  setting  the  goal 
of  its  researches  in  the  future,  to  refrain  from  drawing  conclusions  for  itself 
from  its  larger  or  smaller  treasury  of  observations^  and  from  trying  to  fill  the 
gaps  with  hypotheses.  It  would,  indeed,  be  a  hopeless  proceeding,  if,  in 
order  to  avoid  losing  any  part  of  our  possessions,  we  should  refuse  to 
acquire  any  possessions  whatever." — Karl  Ernst  Baer  (1819). 

Among  the  vegetative  organs  of  the  human  body,  to  the 
development  of  which  we  now  turn  our  attention,  the  intes- 
tinal canal  is  the  most  important.  For  the  intestinal  tube 
is  the  oldest  of  all  the  organs  of  the  animal  body,  and 
carries  us  back  to  the  earliest  time  of  organological  differ- 
entiation, to  the  first  period  of  the  Laurentian  Epoch.  As 
we  have  already  seen,  the  result  of  the  first  division  of 
labour  in  the  homogeneous  cells  of  the  earliest  many-celled 
animal  body  must  have  been  the  formation  of  a  nutritive 
intestinal  canal.  The  first  duty  and  the  first  need  of  every 
organism  is  self-support.  This  task  is  accomplished  by  the 
two  functions  of  nutrition  and  of  the  covering  of  the  body. 
When,  therefore,  in  the  primaeval  collection  of  homogeneous 
cells  (Synamoebium),  of  the  phylogenetic  existence  of  which 
we  yet  have  evidence  in  the  ontogenetic  developmental 
form  of  the  mulberry-germ  {Morula),  the  several  members 
of  the  community  began  to  divide  the  work  of  life,  they 
were  first  obliged  to  engage  in  two  separate  tasks.  One 
half  modified  into  nutritive  cells,  enclosing  a  digestive 
cavity,  the  intestinal  canal ;  the  other  half,  on  the  contrary, 
developed  into  covering  cells,  forming  the  outer  cover- 
ing of  this  intestinal  canal,  and,  at  the  same  time,  of  the 
whole   body.     Thus  arose  the  first  two   germ-layers :   the 


PRIMITIVE   INTESTINAL   CANAL. 


3*3 


inner,  nutritive,  or  vegetative  layer,  and  the  outer,  covering, 
or  animal  layer. 

If  we  try  to  construct  for  ourselves  an  animal  body  of 
the  simplest  conceivable  form,  possessing  such  a  primitive 
intestinal  canal,  and  the  two  primary  germ-layers  forming 
its  wall,  the  result  is  necessarily  the  very  remarkable 
germ-form  of  the  gastrula,  which  we  have  shown  to  exist 
in   wonderful    uniformity   throughout   the    whole    animal 


Fig.  274. — Gastrula  of  a  Chalk-sponge  (Olynthus)  :  A,  from  outside; 
B,  in  longitudinal  section  through  the  axis  ;  g,  primitive  intestine  ;  0,  primi- 
tive mouth  ;  i,  intestinal  layer,  or  entoderm  ;  e,  skin-layer,  or  exoderm. 

series:  in  the  Sponges,  Sea-nettles  (Acalephce),  Worms, 
Soft-bodied  Animals  (Mollusca),  Articulated  Animals  (A  rthro- 
poda),  and  Vertebrates  (Figs.  174-179,  p.  65).  In  all  these 
various  animal  tribes  the  gastrula  reappears  in  the  same 
entirely  simple  form  (Fig.  274).  Its  whole  body  is  really 
merely  the  intestinal  canal  ;  the  simple  cavity  of  the  body, 
the  digestive    intestinal  cavity,  is  the    primitive  intestine 


314  THE   EVOLUTION   OF   MAN. 

(protogaster,  g)  ;  its  simple  opening,  the  primitive  mouth 
(protostoma,  o),  is  at  once  mouth  and  anus ;  and  the  two 
cell-strata  which  compose  its  wall,  are  the  two  primary 
germ-layers :  the  inner,  the  nutritive,  or  vegetative  germ- 
layer,  is  the  intestinal  layer  (entoderma,  i) ;  and  the  outer, 
covering  layer,  which,  by  means  of  its  cilia,  is  also  the  agent 
of  motion,  is  the  animal  layer,  or  skin-layer  (exoderma,  e). 
This  highly  important  fact,  that  the  gastrula  appears  as  an 
early  larval  condition  in  the  individual  development  of  the 
most  varied  animals,  and  that  this  gastrula  always  exhibits 
the  same  structure,  and  that  the  very  differently  developed 
intestinal  canals  of  the  most  varied  animals,  arises,  onto- 
genetically,  from  the  same  extremely  simple  gastrula- 
intestine,  this  very  important  fact  justifies,  in  accordance 
with  the  fundamental  law  of  Biogeny,  two  conclusions, 
which  involve  important  results,  and  of  which  one  is  general 
and  one  special.  The  general  conclusion  is  an  inductive 
one,  and  may  be  stated  thus :  The  very  variously  formed 
intestinal  canal  of  all  the  different  Intestinal  Animals 
has  developed,  phylogenetically,  from  one  common  and 
extremely  simple  primitive  intestine,  from  the  intestinal 
cavity  of  the  Gastrgea,  that  primaeval  common  parent-form 
which  is  at  the  present  reproduced,  in  accordance  with  the 
fundamental  law  of  Biogeny,  in  the  gastrula.  The  second, 
the  special  conclusion,  which  is  connected  with  the  former, 
is  deductive,  and  may  be  stated  thus :  The  intestinal  canal 
in  Man  as  a  whole  is  homologous  with  the  intestinal  canal 
in  all  other  animals ;  it  has  the  same  original  significance, 
and  has  developed  from  the  same  rudimentary  form.186 

Before  proceeding  to  trace  the  history  of  the  develop- 
ment of  the  human  intestinal  canal  in  detail,   it  will  be 


THE   HUMAN   INTESTINAL  CANAL.  3  I  5 

necessary  briefly  to  get  a  correct  idea  of  the  more 
general  conditions  of  the  formation  of  the  intestinal  canal 
in  the  developed  Man.  Not  until  this  is  known  can  the 
development  of  the  several  parts  be  correctly  understood. 
(Cf.  Plates  IV.  and  V.,  vol.  i.  p.  321.)  The  intestinal  canal  in 
the  developed  Man  is,  in  all  essential  points,  exactly  similar 
in  form  to  those  of  all  other  higher  Mammals,  and,  especially, 
to  that  of  the  Catarhines,  the  Narrow-nosed  Apes  of  the 
Old  World.  The  entrance  to  the  intestinal  canal  is  the 
mouth-opening  (Plate  V.  Fig.  1G,  o).  Food  and  drink  pass 
first  through  this  into  the  mouth-cavity,  in  the  lower  part 
of  which  is  the  tongue.  The  human  mouth-cavity  is  hedged 
with  thirty-two  teeth,  attached  in  two  rows  to  the  two  jaws, 
the  upper  and  lower.  It  has  already  been  stated  that  the 
series  of  teeth  is  formed  in  Man  exactly  as  in  the  Catarhine 
Apes,  but  differs  from  the  corresponding  part  in  all  other 
animals  (p.  173).  Above  the  mouth-cavity  is  the  double 
nose-cavity ;  the  two  parts  of  this  are  separated  by  the  par- 
tition-wall of  the  palate.  But,  as  we  have  seen,  the  nasal 
cavity  is  not  originally  separated  at  all  from  the  mouth- 
cavity,  a  common  nasal  and  mouth  cavity  being  primarily 
formed  in  the  embryo,  and  this  separates  at  a  later  period 
into  two  separate  stories  by  the  hard  palate-roof :  the  upper 
is  the  nasal  cavity,  the  lower  is  the  mouth-cavity.  The  nasal 
cavity  is  connected  with  certain  air-filled  bony  cavities ; 
the  jaw-cavities  in  the  upper  jaw,  the  frontal  cavities  in 
the  frontal  bone,  and  the  sphenoid  cavities  in  the  sphenoid 
bone.  Numerous  glands  of  various  kinds  open  into  the 
mouth-cavity,  particularly  many  small  mucous  glands  and 
three  pairs  of  large  salivary  glands. 

The  human  mouth-cavitv  is  half  closed  at  the  back  by 


3l6  THE   EVOLUTION   OF   MAN. 

the  vertical  curtain  which  we  call  the  soft  palate,  and  in 
the  centre  of  the  lower  part  of  which  is  situated  the 
uvula.  A  glance  Avith  the  mouth  open  into  a  mirror  is 
sufficient  to  show  the  form.  The  uvula  is  of  importance, 
because  it  occurs  only  in  Men  and  in  Apes.  On  both  sides 
of  the  soft  palate  are  the  tonsils  (tonsillw).  Through  the 
gate-like  arched  opening  situated  beneath  the  soft  palate, 
we  pass  into  the  throat-cavity  ('pharynx;  Plate  V.  Fig. 
16,  sh),  which  lies  behind  the  mouth-cavity.  This  is  only 
partly  visible  in  the  open  mouth  when  reflected  in  the 
mirror.  Into  the  throat-cavity  a  narrow  passage  opens  on 
each  side  (the  Eustachian  tube  of  the  ear),  which  leads 
directly  into  the  tympanic  cavity  of  the  ear  (Fig.  244,  e, 
p.  2G0).  The  throat-cavity  is  continued  into  a  long- 
narrow  tube,  the  gullet  (oesophagus,  sr).  Through  this 
the  masticated  and  swallowed  food  passes  down  into  the 
stomach.  The  wind-pipe  (trachea,  Ir)  also  opens  into  the 
upper  part  of  the  throat,  and  leads  thence  to  the  lungs. 
The  opening  of  this  is  protected  by  the  epiglottis,  over 
which  the  food  passes.  The  respiratory  organs,  the  two 
lungs  (Plate  IV.  Fig.  8,  lu),  are  situated,  in  Man,  as  in  all 
Mammals,  in  the  right  and  left  sides  of  the  breast-cavity 
(thorax),  and  midway  between  them  is  the  heart  (Fig. 
8,  hr,  hi).  At  the  upper  end  of  the  wind-pipe  (trachea), 
below  the  epiglottis  just  spoken  of,  is  a  peculiarly  differ- 
entiated section,  the  larynx,  which  is  protected  by  a  carti- 
laginous frame.  The  larynx  is  the  most  important  organ 
of  the  human  voice  and  speech,  and  also  develops  from  a 
part  of  the  intestinal  canal.  In  front  of  the  larynx  lies  the 
thyroid  gland  (thyreoidea),  which  occasionally  enlarges  to 
the  so-called  "  goitre." 


THE   HUMAN   INTESTINAL  CANAL. 


317 


The  gullet  (oesophagus)  passes  downward  through  the 
thorax,  along  the  vertebral  column,  behind  the  lungs  and 
the  heart,  and  enters  the  ventral  cavity,  after  penetrating 
the  diaphragm.  The  latter  (Fig.  16,  z)  is  a  membranous, 
muscular,  transverse  partition,  which  in  all  Mammals  (and 
only  in  these)  completely  separates  the  chest-cavity 
(thorax,  c,)  from  the  ventral  cavity  (c„).  As  has  been  said, 
this  division  does  not  originally  exist;  at  first  a  common 
chest  and  ventral  cavity,  the  cceloma,  or  the  pleuro- 
peritoneal  cavity,  is  formed  in  the  embryo.  It  is  only 
afterwards  that  the  diaphragm  forms  a  muscular,  horizontal 
partition  between  the  chest  and  the  ventral  cavities.  This 
partition  then  completely  separates  the  two  cavities,  and 
is  penetrated  only  by  separate  organs,  passing  through  the 


Fig.  275. — Human  stomach  and  gall-intestine  in  Longitudinal  section: 
o,  cardia  (limit  of  the  oesophagus) ;  b,  fundus  (blind  sac  of  the  left  side)  ; 
r,  pylorus  fold;  d,  pylorus  valve;  e,  pylorus-cavity ;  fg  h,  gall-intestine  ; 
i,  mouth  of  the  gall-duct  and  of  the  pancreas  duct.     (After  H.  Meyer.) 

chest-cavity  into  the  ventral  cavity.  One  of  the  most 
important  of  these  organs  is  the  gullet  (oesophagus).  After 
this  has  passed  through  the  diaphragm  into  the  ventral 
cavity   it   enlarges   into  the   stomach    in   which    digestion 


318  THE   EVOLUTION   OF   MAN. 

especially  takes  place.  The  stomach  of  an  adult  man 
(Fig.  275,  Plate  V.  Fig.  16,  rng)  is  an  oblong  sac,  placed 
somewhat  obliquely,  the  left  side  of  which  widens  into 
a  blind-sac,  the  base  of  the  stomach  or  fundus  (b),  while  the 
right  side  narrows,  and  passes  at  the  right  end,  called 
the  pylorus  (e),  into  the  small  intestine.  Between  these  two 
parts  of  the  intestine  is  a  valve,  the  pyloric  valve  (d),  which 
only  opens  when  the  food-pulp  (chyme)  passes  from  the 
stomach  into  the  small  intestine.  The  stomach  itself  is  the 
most  important  digestive  organ,  and  serves  especially  to 
dissolve  the  food.  The  muscular  wall  of  the  stomach  is 
comparatively  thick,  and,  on  the  outside,  has  strong  muscle- 
layers,  which  effect  the  digestive  movements  of  the 
stomach  ; — on  the  inside,  it  has  a  great  number  of  small 
glands,  the  gastric  glands,  which  secrete  the  gastric  juice. 

Next  to  the  stomach  follows  the  longest  part  of  the 
whole  intestinal  canal,  the  central,  or  small  intestine 
(chylog  aster).  Its  principal  function  is  to  effect  the  absorp- 
tion of  the  fluid  mass  of  digested  food,  or  the  food-pulp 
(chyme),  and  it  is  again  divided  into  several  sections,  the 
first  of  which,  the  one  immediately  following  the  stomach, 
is  called  the  gall-intestine,  or  "  twelve-finger  intestine " 
(duodenum,  Fig.  275,  fg  h).  The  gall-intestine  forms  a  short 
loop  curved  like  a  horse-shoe.  The  largest  glands  of  the 
intestinal  canal  open  into  it :  the  liver,  the  most  important 
digestive  gland,  which  furnishes  the  bile,  or  gall,  and  a  very 
large  salivary  gland,  the  ventral  salivary  gland,  or  pancreas, 
which  secretes  the  digestive  saliva.  Both  of  these  glands 
pour  the  juices  they  secrete,  the  bile  and  pancreatic  juice, 
into  the  duodenum  (i)  near  each  other.  In  adults  the  liver 
is  a  very  large  gland,  well  supplied  with  blood,  lying  on  the 


THE   HUMAN   INTESTINAL   CANAL.  319 

right  side,  immediately  below  the  diaphragm,  and  separated 
by  the  latter  from  the  lungs  (Plate  V.  Fig.  16,  lb).  The 
pancreas  lies  somewhat  further  back  and  more  to  the 
left  (Fig.  16,  p).  The  small  intestine  is  so  long  that  it 
has  to  lie  in  many  folds  in  order  to  find  room  in  the  limited 
space  of  the  ventral  cavity ;  these  coils  are  the  bowels. 
They  are  divided  into  an  upper  intestine,  called  the  empty 
intestine  {jejunum),  and  a  lower,  the  crooked  intestine 
(ilium).  In  this  latter  part  lies  that  part  of  the  small 
intestine  at  which,  in  the  embryo,  the  yelk-sac  opens  into 
the  intestinal  tube.  This  long,  thin  intestine  then  passes 
into  the  large  intestine,  from  which  it  is  separated  by  a 
peculiar  valve.  Directly  behind  this  "  Bauhinian  valve " 
the  first  part  of  the  large  intestines  forms  a  broad  pouch- 
like expansion,  the  blind  intestine  (caecum),  the  atrophied 
exti'emity  of  which  is  a  well-known  rudimentary  organ,  the 
vermiform  process  (processus  vermiformis).  The  large 
intestine  (colon)  consists  of  three  parts ;  an  ascending  part 
on  the  right,  a  transverse  central  part,  and  a  descending- 
part  on  the  left.  The  latter  finally  curves  like  an  S,  called 
the  "sigmoid  flexure,"  into  the  last  part  of  the  intestinal 
canal,  above  the  rectum,  which  opens  at  the  back  by  the 
anus  (Plate  V.  Fig.  16,  a).  Both  the  large  intestine  and 
the  small  intestine  are  furnished  with  numerous  glands, 
most  of  them  very  small,  and  which  secrete  mucous  and 
other  juices. 

Along  the  greater  part  of  its  length  the  intestinal  canal 
is  attached  to  the  inner  dorsal  surface  of  the  ventral  cavity, 
or  to  the  lower  surface  of  the  vertebral  column.  It  is 
fastened  by  means  of  the  thin,  membranous  plate,  called  the 

mesentery,   which   develops    directly   under  the  notochord 
37 


320  THE   EVOLUTION   OF   MAN. 

from  the  intestinal-fibrous  layer,  at  the  point  where  this 
curves  into  the  outer  lamina  of  the  side-layer,  into  the 
skin-fibrous  layer  (Plate  IV.  Fig.  5,  g).  The  curving-point 
was  distinguished  as  the  middle-plate  (Fig.  99,  mp).  The 
mesentery  is,  at  first,  very  short  (Plate  V.  Fig.  14i,g);  but  it 
soon  lengthens  considerably  at  the  central  part  of  the  intes- 
tinal canal,  and  takes  the  form  of  a  thin,  transparent, 
membranous  plate,  which  has  to  be  the  more  extended  the 
further  the  folds  of  the  intestine  diverge  from  the  place 
where  they  are  first  attached  to  the  vertebral  column.  The 
blood-vessels,  lymphatic  vessels,  and  nerves  which  enter 
"  the  intestinal  canal  traverse  this  mesentery. 

Although,  therefore,  the  intestinal  canal,  in  the  adult 
human  being  forms  an  extremely  complex  organ,  and 
though  it  shows  in  its  details  so  many  intricate  and  delicate 
structural  arrangements, — into  which  we  cannot  enter 
here, — this  entire  structure  has  developed,  historically, 
from  that  simplest  form  of  primitive  intestine  which 
was  possessed  by  our  gastrcead  ancestors,  and  which  the 
extant  gastrula  now  exhibits.  We  have  already  shown'  (in 
Chapter  VIII.)  that  the  peculiar  Hood-gastrula  (Amphi- 
gastrula)  of  Mammals  (Fig.  277)  may  be  referred  back 
to  the  original  Bell-gastrula  (Archigastrida)  form,  which, 
among  Vertebrates,  is  now  accurately  retained  solely  by 
the  Amphioxus  (Fig.  276  ;  Plate  X.  Fig.  10). 

Like  the  latter,  the  gastrula  of  Man  and  of  all  Mam- 
mals must  be  regarded  as  the  ontogenetic  reproduction 
of  that  phylogenetic  evolution-form  which  we  call  the 
Gastraea,  and  in  which  the  whole  body  of  the  animal  is 
intestine. 

The    peculiar   form    and    mode  in   which    the  complex 


DEVELOPMENT  OF    THE   INTESTINAL  CANAL. 


321 


human  intestinal  canal  develops  from  the  simple  gastrnla 
and  which  is  similar  to  that  in  other  Mammals,  can  there- 
fore be  only  correctly  understood  when  it  is  considered  in 
the  light  of  Phylogeny.     We  must,  accordingly,  distinguish 


Fig.  276. — Archigastrula  of  Amphioxns  (in  longitudinal  section) :  (/, 
primitive  intestine;  0,  primitive  mouth;  *,  intestinal  layer;  e,  skin-layer. 

Fig.  277. — Amphigastrula  of  Mammal  (in  longitudinal  section).  The 
primitive  intestine  (d)  and  primitive  mouth  (o)  are  filled  up  by  the  cells  of 
the  intestinal  layer  (t)  ;  e,  skin-layer. 

between  the  original  primary  intestine  ("the  primitive 
intestine,  or  protogaster ")  of  the  Skull-less  Animals 
(Acrania),  and  the  differentiated  or  secondary  intestine 
("after  intestine,  or  metagaster")  of  the  Skulled  Animals 
(Craniota).  The  intestine  of  the  Amphioxus  (the  repre- 
sentative of  the  Acrania)  forms  no  yelk-sac,  and  develops, 
palingenetically,  from  the  entire  primitive  intestine  of  the 
crastrula.  The  intestine  of  the"  Skulled  Animals,  on  the 
other  hand,  has  a  modified,  kenogenetic  form  of  evolution, 
and  differentiates  at  a  very  early  period  into  two  different 
parts  :  into  the  permanent  secondary  intestine,  which  alone 


322  THE   EVOLUTION   OF   MAN. 

gives  rise  to  the  various  parts  of  the  differentiated  intestinal 
system,  and  the  transient  yelk-sac,  which  serves  only  as  a 
storehouse  of  materials  for  the  building  of  the  embryo. 
The  yelk-sac  attains  its  greatest  development  in  Primitive 
Fishes  (Selachii),  Bony  Fishes  (Teleostei),  Reptiles,  and 
Birds.  In  Mammals,  and  especially  in  Placental  Animals, 
it  is  atrophied.  The  peculiar  intestinal  development  of  the 
Cyclostomi,  Ganoids,  and  Amphibia  must  be  regarded  as 
an  intermediate  form,  between  the  palingenetic  intestinal 
development  of  the  Skull-less  animals,  and  the  kenoge- 
netic  intestinal  development  of  the  Amnion  Animals  (im- 
niota).181 

We  have  already  seen  in  what  a  peculiar  way  the 
development  of  the  intestine  takes  place  ontogenetically  in 
the  human  embryo  and  in  that  of  other  Mammals.  Imme- 
diately from  the  gastrula  of  these  originates  a  globular 
intestinal  germ-vesicle  (gastrocystis),  filled  with  fluid  (Figs. 
72,  73,  vol.  i.  p.  289).  In  the  wall  of  this  is  formed  the 
lyre-shaped  germ-shield,  on  the  lower  side  of  which,  along 
the  middle  line,  appears  a  shallow  groove,  the  first  rudi- 
ment of  the  future,  secondary  intestinal  tube. 

This  intestinal  groove  grows  constantly  deeper,  and  its 
edges  curve  toward  each  other,  to  grow  together  at  last  and 
form  a  tube  (Fig.  100,  vol.  i.  p.  333).  The  wall  of  this 
secondary  intestinal  tube  consists  of  two  membranes  of  the 
inner,  intestinal-glandular  layer,  and  of  the  outer,  intestinal- 
fibrous  layer.  The  tube  is  completely  closed  at  the  ends, 
having  only  an  opening  in  the  centre  of  the  lower  wall, 
by  which  it  is  connected  with  the  intestinal  germ-vesicle 
(Plate  V.  Fig.  14).  The  latter,  in  the  course  of  development, 
becomes  continually  smaller,  as  the  intestinal  canal  continues 


DEVELOPMENT   OF   THE    INTESTINAL  CANAL.  323 

to  grow  larger  and  more  perfect.  While,  at  first,  the  intes- 
tinal tube  appears  only  as  a  little  appendage  on  one  side  of 
the  great  intestinal  germ-vesicle  (Fig.  278),  the  remnant  of 
the  latter  afterwards  forms  only  a  very  inconsiderable  appen- 
dage of  the  great  intestinal  canal.  This  appendage  is  the 
yelk-sac,  or  navel-vesicle.  It  entirely  loses  its  importance, 
and  at  length  disappears,  while  the  intestinal  canal  is  finally 
closed  at  the  original  central  opening,  where  it  forms  the 
so-called  intestinal  navel  (Fig.  94,  vol.  i.  p.  312). 

It  has  also  been  said  that  this  simple  cylindrical  intestinal 
tube,  in  Man  as  in  all  Vertebrates,  is  at  first  entirely  closed 
at  both  ends  (Plate  V.  Fig.  14),  and  that  the  two  permanent 
openings  of  the  intestinal  canal — at  the  anterior  extremity, 
the  mouth,  at  the  posterior,  the  anus — form  only  second- 
arily, and  from  the  outer  skin.  At  the  fore  end,  a  shallow 
mouth-furrow  originates  in  the  outer  skin,  and  this  grows 
toward  the  blind,  anterior  end  of  the  head  intestinal  cavity, 
into  which  it  finally  breaks.  In  the  same  way  a  shal- 
low furrow  for  the  anus  is  formed  behind  in  the  skin, 
and  this  soon  grows  deeper,  and  grows  toward  the  blind 
posterior  end  of  the  pelvic  intestinal  cavity,  with  which  it 
finally  unites.  At  both  extremities  there  is,  at  first,  a  thin 
partition  between  the  outer  skin-furrow  and  the  blind  end 
of  the  intestine,  and  this  disappears  when  the  opening  is 
made.188 

Directly  in  front  of  the  anus  the  allantois  grows  out  of 
the  posterior  intestine ;  this  is  the  important  embryonic 
appendage  which  develops,  in  Placental  Animals,  and  only 
in  these  (thus  in  Man  too)  into  the  placenta  (Figs.  278,  279, 1 ; 
Plate  V.  Fig.  14,  al).  In  this  more  developed  form — repre- 
sented in  the  diagram  (Fig.  94,  ,v  vol.  i.  p.  312) — the  intestinal 


324 


THE   EVOLUTION    OF   MAN. 


canal  of  Man,  like  that  of  all  other  Mammals,  now  forms  a 
slightly-curved,  cylindrical  tube,  which  has  an  opening  at 
both  ends,  and  from  the  lower  wall  of  which  depend  two 
sacs;  the  anterior  navel-bladder,  or  yelk-sac,  and  the  pos- 
terior allantois,  or  primitive  urinary  sac. 

Microscopic  observation  shows  that  the  thin  wall  of  this 
simple  intestinal  tube  and  of  its  two  bladder-like  append- 
ages is  composed  of  two  distinct  cell-strata.  The  inner, 
which  coats  the  entire  cavity,  consists  of  larger,  darker  cells, 


Fig.  278. — Human  embryo  of  the  third  week,  with  the  amnion  and 
allantois.  The  great  globular  yelk-sac  is  below,  the  bladder-like  allantois 
on  the  right ;  there  are  as  yet  no  limbs.  The  germ,  with  its  appendages,  is 
enclosed  in  the  tufted  membrane  (chorion). 

Fig.  279. — Human  embryo,  with  amnion  and  allantois,  in  the  fourth 
week.  (After  Krause.)  The  amnion  (w)  lies  pretty  close  to  the  body.  The 
greater  part  of  the  yelk-sac  (d)  has  been  torn  away.  Behind  this  the  allan- 
tois appears  as  a  small  pear-shaped  bladder.  Arms  (/)  and  legs  (b)  are 
already  commenced:  v,  fore-brain;  z,  twixt-brain ;  m,  mid-brain;  h,  hind- 
brain  ;  n,  after-brain ;  a,  eye ;  k,  three  gill-arches ;  c ,  heart ;  s,  tail. 


RUDIMENT   OF   THE   INTESTINAL    CANAL.  325 

and  is  the  intestinal-glandular  layer.  The  outer  stratum 
consists  of  lighter,  smaller  cells,  and  is  the  intestinal  fibrous- 
layer.  The  cavities  of  the  mouth  and  the  anus  are  the  only 
exceptions  to  this,  because  they  originate  from  the  outer 
skin.  The  inner  cell-coating  of  the  entire  mouth-cavity  is 
therefore  furnished,  not  by  the  intestinal  glandular-layer, 
but  by  the  skin-sensory  layer,  and  its  muscular  lower  layer, 
not  by  the  intestinal-fibrous  layer,  but  by  the  skin-fibrous 
layer.  This  is  equally  true  of  the  wall  of  the  anal  cavity 
(Plate  V.  Fig.  15). 

If  the  question  be  asked,  what  relation  these  component 
germ-layers  of  the  primitive  intestinal  wall  bear  to  the 
infinitely  varied  tissues  and  organs  which  we  afterwards 
find  in  the  developed  intestine,  the  answer  is  extremely 
simple.  The  relations  of  these  two  layers  to  the  formation 
and  differentiation  of  the  tissues  of  the  intestinal  canal  with 
all  its  parts,  may  be  condensed  into  a  single  sentence :  The 
intestinal  epithelium,  that  is,  the  inner,  soft  cell-stratum 
which  coats  the  cavities  of  the  intestinal  canal  and  of  all  its 
appendages,  and  which  directly  accomplishes  the  nutritive 
process,  develops  solely  from  the  intestinal-glandular 
layer ;  on  the  contrary,  all  other  tissues  and  organs  belong- 
ing to  the  intestinal  canal  and  its  appendages,  proceed  from 
the  intestinal-fibrous  layer.  From  this  latter,  therefore, 
originates  the  entire  outer  covering  of  the  intestinal  tube 
and  its  appendages  ;  the  fibrous  connective  tissue  and  the 
smooth  muscles  which  compose  its  fleshy  skin ;  the  carti- 
lages which  support  these,  for  example,  the  cartilage  of  the 
larynx  and  of  the  trachea ;  the  numerous  blood  and  lymph 
vessels  which  absorb  nutrition  from  the  wall  of  the  intestine; 
in    short,  everything   belonging  to  the  intestine,  with  the 


/ 

326  THE    EVOLUTION    OF   MAN. 

exception  of  the  intestinal  epithelium.  From  the  intestinal- 
fibrous  layer  originates  also  the  entire  mesentery  with  all 
the  adjacent  parts,  the  heart,  the  large  blood-vessels  of  the 
body,  etc.  (Plate  V.  Fig.  16). 

Let  us  now  turn  aside  for  a  moment  from  this  original 
rudimentary  intestine  of  Mammals,  in  order  to  institute  a 
comparison  between  it  and  the  intestinal  canal  of  those 
lower  Vertebrates  and  Worms,  which  we  have  learned  to 
recognize  as  the  ancestors  of  Man.  In  the  simplest  Gliding- 
worm,  or  Turbellaria  (Rhabdoccelum,  Fig.  280),  we  find  a 
very  simple  intestinal  form.  As  in  the  gastrula,  the  intes- 
tine in  these  Worms  is  a  simple  pouch  with  a  single  open- 
ing, which  latter  acts  both  as  mouth  and  anus  (m).  The 
intestinal  pouch  has,  however,  differentiated  into  two  sec- 
tions, an  anterior  throat-intestine  (sd)  and  a  posterior 
stomach-intestine  (d).  This  differentiation  becomes  more 
important  in  the  Ascidia  (Fig.  281)  and  in  the  Amphioxus 
(Fig.  282),  which  connects  the  Worms  with  the  Vertebrates. 
In  these  two  animal  forms  the  intestine  is  essentially 
identical ;  the  anterior  portion  forms  the  respiratory  gill- 
intestine,  the  posterior  forms  the  digestive  stomach-intes- 
tine. In  both  it  develops,  palingenetically,  directly  from  the 
primitive  intestine  of  the  gastrula  (Plate  XL  Figs.  4,  10). 
But  the  original  mouth-opening  of  the  gastrula,  or 
the  primitive  mouth,  afterwards  closes,  and  in  its  place  is 
formed  the  later  anus.  In  the  same  way,  the  mouth- 
opening  of  the  Amphioxus  and  of  the  Ascidian  is  a  new 
formation,  as  is  the  mouth-opening  of  Man,  and  generally, 
of  all  Skulled  Animals  (Oraniota).  The  secondary  forma- 
tion of  the  mouth  of  the  Lancelet  is  connected,  as  may  be 
conjectured  with  some  probability,  with  the  formation  of 


EARLV   FORMS  OF  THE   INTESTINAL   CANAL. 


327 


the  gill-openings,  which  appear  directly  behind  it  on  the 
intestine.      The   front   portion   of  the   intestine   has   thus 


Fig.  280. — A  simple  Gliding  Worm  (Rhabdocoslum)  m,  mouth;  sd,  throat- 
epithelium  ;  sui,  throat  muscle-mass  ;  J,  stomach-intestine;  nc,  renal  ducts  ; 
/,  ciliated  outer-skin;  mm,  openings  of  the  latter  ;  au,  eye;  na,  nose-pit. 

Fig.  281. —  Structure  of  an  Ascidian  (seen  from  the  left  side,  as  in  Plate 
XI.  Pig.  14).  The  dorsal  side  is  turned  toward  the  right,  the  ventral  side  to 
tin'  left;  the  mouth-opening  (0)  is  above;  at  the  opposite,  tail  end,  the 
ascidian  has  become  adherent.  The  gill-intestine  (br),  perforated  by  many 
openings,  extends  into  the  stomach-intestine.  Tho  terminal  intestine 
opens  through  the  anus  (a)  into  the  gill-cavity  (cl),  from  which  the  excre- 
ment is  passed  out  with  the  respirated  water  through  the  gill-pore,  or  cloacal 
opening  (a*)  j   m.  mantle.     (After  Gegenbaur.) 


328 


THE   EVOLUTION    OF   MA.N. 


become  a  respiratory  organ.  I  have  already  pointed  out 
how  characteristic  this  adaptation  is  of  Vertebrates  and 
Mantle  Animals  (Tunicata,  p.  87).  The 
phylogenetic  origin  of  the  gill-openings  in- 
dicates the  beginning  of  a  new  epoch  in 
the  tribal  history  of  Vertebrates. 

The  most  important  process  we  meet 
with  in  the  further  ontogenetic  development 
of  the  intestinal  canal  in  the  human  embryo, 
is  the  origin  of  the  gill-openings.  At  the 
head  of  the  human  embryo,  the  wall  of  the 
throat  very  early  unites  with  the  outer  wall 
of  the  body,  and  four  openings  then  form 
on  the  right  and  left  sides  of  the  neck, 
behind  the  mouth,  and  these  lead  directly 
from  without  into  the  throat-cavity.  These 
openings  are  the  gill-openings,  and  the  par- 
titions separating  them  are  the  gill-arches 
(Figs.  116-118,  vol.  i.  p.  356;  Plates  I. 
and  V.,  Fig.  15,  ks).  These  embryonic  for- 
mations are  very  interesting ;  for  they  show 

Fig.  282. —  Lancelet  (Amphioxus  lanceolatus) ,  double 
the  natural  size,  seen  from  the  left  side  (the  longi- 
tudinal axis  is  perpendicular,  the  mouth  end  above, 
the  tail  end  below  (as  in  Plate  XL  Fig.  15)  :  a,  mouth- 
opening,  surrounded  by  bristles ;  b,  anal  opening ;  c, 
gill-pore  (porus  hranchialis)  ;  d,  gill-body;  <?,  stomach; 
/,  liver ;  g,  small  intestine ;  h,  gill-cavity  ;  i,  notochord, 
below  which  is  the  aorta ;  k,  aortal  arch ;  7,  main  stem 
of  the  gill-artery ;  m,  swellings  on  the  branches  of 
the  latter;  n,  hollow  vein  ;   o,  intestinal  vein. 


that  all  the  higher  Vertebrates  when  in  a  very  young  state, 


ORIGIN   OF   THE   GILL-OPENINGS.  329 

reproduce,  in  accordance  with  the  fundamental  principle  of 
Biogeny,  the  same  process  which  was  originally  of  the 
greatest  importance  to  the  development  of  the  whole  verte- 
brate tribe.  This  process  was  the  differentiation  of  the 
intestinal  canal  into  two  sections :  an  anterior,  respiratory 
part,  the  gill-intestine,  which  serves  only  for  breathing, 
and  a  posterior,  digestive  part,  the  stomach-intestine,  which 
serves  only  for  digestion.  As  we  meet  with  this  very 
characteristic  differentiation  of  the  intestinal  tube  into  two, 
physiologically,  very  distinct  main  sections,  not  only  in 
the  Amphioxus,  but  also  in  the  Ascidian  and  the  Appen- 
dicularia,  we  can  safely  conclude  that  it  also  existed  in 
our  common  ancestors,  the  Chorda  Animals  (Chordoma), 
especially  as  even  the  Acorn  Worm  (Balanoglossus)  has 
it  (Fig.  186,  p.  86).  All  other  Invertebrate  Animals  are 
entirely  without  this  peculiar  arrangement. 

The  number  of  the  gill-openings  is  still  very  large  in  the 
Amphioxus,  as  in  Ascidians  and  in  the  Acorn  Worm.  In 
the  Skulled  Animals  it  is,  on  the  contrary,  very  much 
lessened.  Fishes  mostly  have  from  four  to  six  pairs  of  o-ill- 
openings.  In  the  embryos  of  Man  and  the  higher  Verte- 
brates also,  only  three  or  four  pairs  are  developed,  and  these 
appear  at  a  very  early  period.  The  gill-openings  are  perma- 
nent in  Fishes,  and  afford  a  passage  to  the  water  which  has 
been  breathed  in  through  the  mouth  (Figs.  191,  192,  p.  113 ; 
Plate  V.  Fig.  13,  ks).  On  the  other  hand,  the  Amphibians 
lose  them  partially,  and  all  the  higher  Vertebrates  entirely. 
In  the  latter,  only  a  single  vestige  of  the  gill-openings  remains, 
the  remnant  of  the  first  gill-opening.  This  changes  into  a 
part  of  the  organ  of  hearing ;  from  it  originates  the  outer 
ear-canal,  the  tympanic  cavity,  and  the  Eustachian  tube. 


00^ 


TABLE    XXXVI. 

Systematic  Survey  of  the  Development  of  the  Human  Intestinal  System. 
N.B.—  The  parts  marked  thus  f  are  processes  from  the  intestinal  tube. 


First  main  section 
of  the 

Intestinal 

System : 

the  Respiratory 

Intestine 

(Gill  Intestine). 

Pneogaster. 

(Tractus 
respiratorius.) 


II. 

Second  main 
section  of  the 

Intestinal 
System : 
Digestive 
Intestine 
(Stomach  Intes- 
tine). 
Pepiogaster. 
{Tractus 
digestivus.) 


1.  Mouth-cavity 
{Cavum  oris) 


Nose-cavity 
{Cavum  nasi) 


Throat-cavity 
{Cavum  pharyn- 
gis) 


Lung-cavity 
,        {Cavum  pulmon 


Mouth-opening 

Lips 

Jaws 

Teeth 

Tongue 
I     Tongue  bone 
I  f  Salivary  glands 

Soft  palate 
V    Uvula 

l    Nose  canal 
I  f  Jaw  cavities 
|  f  Frontal  cavities 
[f  Ethmoid  cavity 

Isthmus  of  the  throat 

Tonsils 

Pharynx 
t  Eustachian  tube 
f  Tympanic  cavity 
t  Brain-appendage 
f  Thyroid  gland 

•  f  Larynx 

pipe 


C  t  Larynx 

is)  \  +  WindPi 
IS>  I  f  Lungs 


Anterior  Intestine 
{Prosogaster) 


6.  Central  Intestine 
{Mesogaster) 


1.  Posterior  Intestine 
{Epigaster) 


Urinary  Intestine 
\         {Urogaster) 


Gullet 

Stomach-opening 
Stomach 
Stomach  exit 

Gall-intestine 
+  Liver 
f  Pancreas 

Empty  intestine 
(f  Yelk-sac,    or    navel- 
bladder) 

Crooked  intestine 

Large  intestine 
+  Blind  intestine 
f  Vermiform  process  of 
the  coecum 

Rectum 

Anal  opening 

(+  Primitive  urinary  sac 
"rinary  tube 
Urinary  bladder 


Rima  oris 

Labia 

Maxilltz 

Dentes 

Lingua 

Os  hyoides 

Glandules  salivates 

Velum  palatinum 

Uvula 


ill 
'If 

*  3 


Meatus  narium 
Sinus  maxillares 
Sinus  frontales 
Sinus  ethmoidales  }  3 

Isthmus  fauciuta, 

Tonsillar 

Pharynx 

Tuba  Eustachii 

Cavum  tympani 

Hypophysis 

Thyreoidea 


Larynx 

Trachea 
Pulmones 

(Esophagus 
Cardia 
Stomachus 
Pylorus 

Duodenum 

Hepar 

Pancreas 

Jejunum 

( Vesicula  umbilica- 

lis) 
Ileum 

Colon 

Coecum 

Processus      vermi- 

formis 
Rectum 
Anus 

Allanlois) 

Urethra 

Urocystis 


8^ 


THE  MOUTH-SKELETON.  33 1 

We  have  already  considered  this  remarkable  formation,  and 
will  only  call  attention  once  more  to  the  interesting  fact  that 
the  human  middle  and  external  ear  is  the  last  remnant 
of  the  gill-opening  of  a  Fish.  The  gill-arches,  also,  which 
separate  the  gill-openings,  develop  into  very  various  parts. 
In  Fishes  they  remain  permanently  as  gill-arches,  carrying 
the  respiratory  gill-tufts ;  so  also  in  the  lowest  Amphibia ; 
but  in  the  higher  Amphibia  they  undergo  various  modifica- 
tions in  the  course  of  development,  and  in  all  the  three 
higher  vertebrate  classes,  thus  also  in  Man,  the  tongue-bone 
(os  hyoicles)  and  the  bonelets  of  the  ear  originate  from  the 
gill-arches.     (Cf.  Plates  VI.  and  VII.) 

From  the  first  gill-arch,  from  the  centre  of  the  inner 
surface  of  which  the  muscular  tongue  grows,  proceeds 
the  rudimentary  jaw-skeleton ;  the  upper  and  lower  jaws 
which  enclose  the  cavity  of  the  mouth  and  carry  the 
teeth.  The  Acrania  and  Monorhina  are  entirely  destitute 
of  these  important  parts.  They  first  appear  in  the  genuine 
Fishes,  and  have  been  transmitted  by  these  to  the  higher 
Vertebrates.  The  original  formation  of  the  human  mouth- 
skeleton,  of  the  upper  and  lower  jaws,  can  thus  be  traced 
back  to  the  earliest  Fishes,  from  which  we  have  inherited 
them.  The  teeth  originate  from  the  outer  skin-covering 
which  covers  the  jaws ;  for,  as  the  formation  of  the  whole 
mouth-cavity  takes  place  from  the  outer  germ-layer,  the  teeth 
must,  of  course,  also  have  developed  originally  from  the  skin- 
layer.  This  can  be  actually  proved  by  close  microscopic 
examination  of  the  most  delicate  structural  features  of  the 
teeth.  The  scales  of  Fishes,  especially  of  Sharks,  are,  in 
this  respect,  exactly  similar  to  their  teeth  (Fig.  283).  Thus 
the  human  teeth,  in  their  earliest  origin,  are  modified  fish- 


332 


THE   EVOLUTION   OF   MAN. 


scales.188  On  similar  grounds  we  must  regard  the  salivary 
glands,  which  open  into  the  mouth-cavity,  as  really  outer- 
skin  (epidermic)  glands,  which  have  not  developed,  like  the 
other  intestinal  glands,  from  the  intestinal-glandular  layer 
of  the  intestinal  canal,  but  from  the  outer  skin,  from  the 
horn-plate  of  the  outer  germ-layer.  It  is  evident  that,  as 
the  mouth  develops  in  this  way,  the  salivary  glands  must 
be  placed  genetically  in  the  same  series  with  the  sweat, 
sebaceous,  and  milk  glands  of  the  epidermis. 

^l/jf\W  ^\(]-J  ^ie  numan  intestinal  canal  is 

(' W  iM  (     therefore   quite    as    simple   in    its 

original  formation  as  the  primitive 

/|*\  intestine  of  the  gastrula.      It  also 

^j/  resembles  that  of  the  lowest  Worms. 

It  then  differentiates  into  two  sec- 

,p^  tions,  an  anterior  gill-intestine,  and 

WW i   (fvf  a  Posterior  stomach-intestine,   like 


v\^7'y|  the  intestinal  canal  of  the  Lancelet 
(A\$);  and  the  Ascidian.      By  the  develop- 
V/\W./j    ment  of  the  jaws   and   gill-arches 
'''^f)  (0   it  is   modified    into   a    true   Fish- 
intestine.    Afterwards,  however,  the 
gill-intestine,  which  is  a  memorial 
of  the   Fish-ancestors,  as   such,  is 
a  entirely  lost.    The  parts  that  remain 
Shark  (Oentrcphorus  calceus).  take  a  wholly  different  form ;   but 

On  eachrhomboid  bone-tablet,  notwithgtandi         ^    ^   anterior 

lying  in  the  leather-skin,  rises  _ 

a  small,  three-cornered  tooth.  Section  of  OUT  intestinal  canal  thus 

(After  Gegenbaur.)  surrenders     entirely      its    original 

form  of  gill-intestine,  it  yet  retains  its  physiological  func- 
tion   as   a    respiratory   intestine;     for   the   extremely   in- 


THE  BREATHING  APPARATUS.  333 

teresting  and  remarkable  discovery  is.  now  made  that  even 
the  permanent  respiratory  organ  of  the  higher  Vertebrates, 
the  air-breathing  lungs,  has  also  developed  from  this  anterior 
section  of  the  intestinal  canal.  Our  lungs,  together  with 
the  wind-pipe  {trachea)  and  the  larynx,  develop  from  the 
ventral  wall  of  the  anterior  intestine.  This  entire  great 
breathing-apparatus,  which  occupies  the  greater  part  of 
the  chest  {thorax)  in  the  developed  Man,  is  at  first  merely 
a  very  small  and  simple  vesicle  or  sac,  which  grows  out 
from  the  intestinal  canal  immediately  behind  the  gills,  and 
soon  separates  into  two  lateral  halves  (Figs.,  284,  c,  285,  c ; 
Plate  V.  Figs.  13,  15,  16,  lu).  This  vesicle  occurs  in  all 
Vertebrates  except  in  the  two  lowest  classes,  the  Acrania  and 
Cyclostomi.  In  the  lower  Vertebrates,  however,  it  develops, 
not  into  lungs,  but  into  an  air-filled  bladder  of  considerable 
size,  occupying  a  great  part  of  the  body-cavity  {cozloma), 
and  which  is  of  quite  a  different  significance  from  the 
lungs.  It  serves,  not  for  breathing,  but  as  an  Irydrostatic 
apparatus :  for  vertical  swimming  movements  it  is  the 
swimming-bladder  of  Fish ;  but  the  lungs  of  Man  and  of 
all  other  air-breathing  Vertebrates  develop  from  the  same 
simple  bladder-like  appendage  of  the  anterior  intestine, 
which,  in  Fishes,  becomes  the  swimming-bladder. 

Originally  this  sac  also  has  no  respiratory  function,  but 
serves  only  as  an  hydrostatic  apparatus,  augmenting  or 
diminishing  the  specific  gravity  of  the  body.  Fishes,  in 
which  the  swimming-bladder  is  fully  developed,  are  able  to 
compress  it,  and  thus  to  condense  the  air  contained  in  it. 
The  air  sometimes  also  escapes  from  the  intestinal  canal 
through  an  air-passage  which  connects  the  swimmino-- 
bladder  with  the  throat  {pharynx),  and  is  expelled  through 


334 


THE    EVOLUTION    OF   MAN. 


the  mouth  ;  in  this  way  the  circumference  of  the  swim- 
ming-bladder is  diminished,  and  the  fish  becomes  heavier 
and  sinks.  When  the  animal  is  again  about  to  ascend, 
the  swimming-bladder  is  distended  by  remitting  the  com- 


^^ 


Fig.  284. — Intestine  of  an  embryonic  Dog  (which  is  representee  in  Fig. 
137,  vol.  i.  p.  382;  after  Bischoff),  from  the  ventral  side  :  a,  gill-arches  (four 
pairs) ;  b,  rudimentary  throat  and  larynx ;  c,  lungs ;  d,  stomach  ;  /,  liver ;  g, 
walls  of  the  opened  yelk-sac,  into  which  the  central  intestine  opens  by  a 
wide  aperture  ;  h,  rectum. 

Fig.  285. — The  same  intestine,  seen  from  the  right  side:  a,  lungs ;  b, 
stomach ;  c,  liver ;  d,  yelk-sac ;  e,  rectum. 

pressing  force.  This  hydrostatic  apparatus  begins  to  be 
transformed  into  a  respiratory  organ  in  the  Mud-fishes 
(Dipneusta),  the  blood-vessels  in  the  wall  of  the  swim- 
ming-bladder no  longer  merely  separating  air,  but  also 
inhaling  fresh  air,  which  has  come  in  through  the  air- 
passage.  This  process  is  fully  developed  in  all  Amphibia. 
The  original  swimming-bladder  here  generally  becomes  a 


EVOLUTION  OF  THE  LUNGS.  335 

lung,  and  its  air-passage  a  wind-pipe.  The  amphibian  lung- 
has  been  transmitted  to  the  three  higher  vertebrate  classes, 
and  even  in  the  lowest  Amphibia  the  lung  on  either  side 
is  as  yet  a  very  simple,  transparent,  thin-walled  sac — as, 
for  instance,  in  our  common  Water-Newts,  or  Tritons,  and 
very  like  the  swimming-bladder  of  Fishes.  The  Amphibia 
have,  it  is  true,  two  lungs,  a  right  and  a  left;  but  in 
many  Fishes  also  (in  the  ancient  Ganoids)  the  swim- 
ming-bladder is  double,  the  organ  being  divided  into  a 
right  and  a  left  half.  On  the  other  hand,  the  lung  of  the 
Ceratodus  is  single  (p.  119).  The  earliest  rudiment  of  the 
lung  in  the  human  embryo  and  in  the  embryo  of  all  higher 
Vertebrates  is  also  a  simple,  single  vesicle,  which  does  not 
separate  till  afterwards  into  a  pair  of  halves — the  right  and 
the  left  lung.  At  a  later  period,  the  two  vesicles  grow  con- 
siderably, occupy  the  greater  part  of  the  chest  cavity,  and  lie 
one  on  each  side  of  the  heart ;  even  in  Frogs  we  tind  that  the 
simple  sac,  in  the  course  of  its  development,  is  transformed 
into  a  spongy  body  of  a  peculiar,  froth-like  texture.  This 
lung-tissue  develops  as  a  tree-like,  branched  gland,  bearing 
berry-like  appendages.  The  process  by  which  the  lung-sac 
was  attached  to  the  anterior  intestine,  which  was  originally 
very  short,  lengthens,  by  simple  growth,  into  a  long  thin 
tube  ;  this  tube  is  the  wind-pipe  {trachea) ;  it  opens  above 
into  the  throat  (pharynx),  and  below  divides  into  two 
branches  which  pass  into  the  two  lungs.  In  the  wall  of  the 
wind-pipe  ring-shaped  cartilages  develop,  which  keep  the 
whole  distended  ;  at  the  upper  end  of  this  wind-pipe,  below 
its  entrance  into  the  throat,  the  larynx,  the  organ  of  voice 
and  speech,  develops.  The  larynx  occurs  even  in  Amphibia 
in  very  various  stages  of  development,  and  with  the  aid  of 


336  THE    EVOLUTION   OF   MAN. 

Comparative  Anatomy  we  can  trace  the  progressive  develop- 
ment of  this  important  organ  from  its  very  simple  rudiment 
in  the  lower  Amphibia  up  to  the  complex  and  vocal  appara- 
tus represented  by  the  larynx  of  Birds  and  Mammals. 

Though  these  organs  of  voice,  speech,  and  air-respiration 
develop  so  differently  in  the  various  higher  Mammals,  they 
yet  all  arise  from  the  same  simple  original  rudiment — 
from  a  vesicle  which  grows  out  of  the  wall  of  the  anterior 
intestine.  We  have  thus  satisfied  ourselves  of  the  interest- 
ing fact  that  both  the  respiratory  apparatus  of  Vertebrates 
develop  from  the  fore  part  of  the  intestinal  canal ;  first,  the 
primary  and  more  primitive  water-respiring  apparatus,  the 
gill-body,  which  is  altogether  lost  in  the  three  higher 
vertebrate  classes ;  and,  afterwards,  the  secondary  and  more 
recent  air-breathing  apparatus,  which  acts  in  Fishes  only 
as  a  swimming-bladder,  but  as  a  lung  from  the  Dipneusta 
upwards. 

We  must  say  a  few  words  about  an  interesting  rudi- 
mentary organ  of  the  respiratory  intestine,  the  thyroid 
gland  (thyreoidea),  the  large  gland  situated  in  front  of  the 
larynx,  and  below  the  so-called  "  Adam's  apple,"  and  which, 
especially  in  the  male  sex,  is  often  very  prominent ;  it  is 
produced  in  the  embryo  by  the  separation  of  the  lower  wall 
of  the  throat  (pharynx).  This  thyroid  gland  is  of  no 
use  whatever  to  man;  it  is  only  aesthetically  interesting, 
because  in  certain  mountainous  districts  it  has  a  tendency 
to  enlarge,  and  in  that  case  it  forms  the  "  goitre "  which 
hangs  from  the  neck  in  front.  Its  dysteleological  interest 
is,  however,  far  higher ;  for  as  Wilhelm  Muller  of  Jena 
has  shown,  this  useless  and  unsightly  organ  is  the  last 
remnant  of  the  "  hypobranchial  groove,"  which  we  have 


THE   STOMACH.  337 

already  considered,  and  which,  in  the  Ascidia  and  in  the 
Amphioxus,  traverses  the  middle  of  the  gill-body,  and  is  of 
great  importance  in  conducting  the  food  into  the  stomach 
('vol.  i.  p.  420;  Plate  XI.  Figs.  14-16,  y).189 

The  second  main  section  of  the  intestinal  canal,  the 
stomach  or  digestive  intestine,  undergoes  modifications  no 
less  important  than  those  affecting  the  first  main  section. 
On  tracing  the  further  development  of  this  digestive  section 
of  the  intestinal  tube,  we  again  find  a  very  complex  and 
composite  organ  eventually  produced  from  a  very  simple 
rudiment.  For  the  sake  of  rendering  the  matter  more 
intelligible,  we  may  distinguish  the  digestive  intestine 
into  three  parts :  the  fore  intestine  (with  the  gullet  and 
stomach) ;  the  middle  intestine,  the  gall-intestine  (with  the 
liver  and  pancreas) ;  the  empty  intestine  (jejunum),  and 
crooked  intestine  (ileus) ;  and  the  hind  intestine  (large 
intestine  and  rectum).  Here  we  again  find  protuberances 
or  appendages  of  the  originally  simple  intestinal  tube 
which  change  into  very  various  structures.  We  have 
already  discussed  two  of  these  appendages — the  yelk-sac, 
which  protrudes  from  the  middle  of  the  intestinal  tube 
(Fig.  286,  c),  and  the  allantois,  which  grows  out  of  the 
last  portion  of  the  pelvic  intestine  as  a  large  sac-like 
protuberance  (u).  The  protuberances  from  the  middle 
of  the  intestine  are  the  two  great  glands  which  open 
into  the  duodenum,  the  liver  (h)  and  the  ventral  salivary 
gland. 

Immediately  behind  the  bladder-like  rudiment  of  the 
lungs  (Fig.  286, 1)  comes  that  portion  of  the  intestinal  tube 
which  forms  the  most  important  part  of  the  digestive 
apparatus,  viz.,  the  stomach  (Figs.  284,  d,  285,  b).     This  sac- 


338 


THE   EVOLUTION   OF   MAN. 


shaped  organ,  in  which  the  food  is  especially  dissolved  and 
digested,  is  not  so  complex  in  structure  in  the  lower  Verte- 
brates as  in  the  higher.  Thus,  for  instance,  in  many  Fishes, 
it  appears  as  a  very  simple  spindle-shaped  expansion  at  the 


Fig.  286. — Longitndinal  section  through  an  embryonic  Chick  on  the 
fifth  day  of  incubation  :  d,  intestine  ;  o,  mouth  ;  a,  anus ;  I,  lungs ;  h,  liver ; 
q,  mesentery ;  v,  auricle  of  heart ;  fc,  ventricle  of  heart ;  b,  arterial  arches ; 
1,  aorta;  c,  yelk-sac ;  vn,  yelk-duct;  u,  allantois;  r,  stalk  of  allantois;  n, 
amnion ;  iv,  aninion-cavity  ;  s,  serous  membrane.     (After  Baer.) 


beginning  of  the  digestive  section  of  the  intestine,  which 
latter  passes  from  front  to  rear  in  a  straight  line  under  the 
spinal  column  in  the  central  plane  of  the  body.  In  Mam- 
mals the  rudiment  of  this  organ  is  as  simple  as  it  thus 
is  permanently  in  Fishes .  but  at  a  very  early  period  the 
various  parts  of  the  stomach-sac  begin  to  develop  unequally. 
As  the  left  side  of  the  spindle-shaped  pouch  grows  much 
more  vigorously  than  the  right,  and  as,  at  the  same  time, 


DEVELOPMENT  OF  THE   STOMACH. 


339 


there  occurs  a  considerable  obliquity  of  its   axis,  it  soon 

assumes  an  oblique  position.     The  upper  end  lies  more  to 

the  left  and  the  lower  end  more 

to  the  right.     The  anterior  end 

extends  so  as  to  form   the  long 

narrow     canal     of     the     gullet 

(oesophagus)  ;    below  the  latter, 

the    blind-sac    of    the    stomach 

(fundus)  bulges  out  to  the  left, 

and  thus  the  later  form  of  the 

stomach  is  gradually  developed 

(Fig.  287,  e ;  Fig.  275,  p.  317).  The 

axis,  which  was  originally  verti- 

Fig.  287. — Hurnau  embryo  of  five 
weeks,  from,  the  ventral  side ;  opened 
(enlarged).  The  breast  wall,  abdominal 
wall,  and  liver,  have  been  removed.  3, 
external  nasal  process  ;  4,  iipper  jaw  ;  5, 
lower  jaw ;  z,  tongue ;  v,  right,  v',  left 
ventricle  of  heart ;  o',  left  auricle  of 
heart ;  b,  origin  of  aorta  ;  V  b"  b'",  1st, 
2nd,  3rd  aorta-arches ;  c  c'  c",  hollow 
vein ;  ae,  lungs  (y,  lung-arteries) ;  e, 
stomach ;  m,  primitive  kidneys  (j,  left 
yelk-vein ;  s,  pyloras ;  a,  right  yelk- 
artery  ;  n,  navel-artery  ;  ?«,  navel-vein) ; 
x,  yelk-duct ;  i,  terminal  intestine ;  8, 
tail;  9,  fore-limb  ;  9',  hind -limb.  (After 
Coste.) 

cal,  now  inclines  from  a  higher  point  on  the  left  to  a  lower 
on  the  right,  and  continually  acquires  a  more  transverse 
direction.  In  the  outer  stratum  of  the  stomach-wall,  and 
from  the  intestinal-fibrous  layer,  develop  the  strong  muscles 
which    perform   the    powerful    digestive    movements.      In 


340  THE   EVOLUTION   OF   MAN. 

the  inner  stratum,  on  the  contrary,  innumerable  minor 
glands  develop  from  the  intestinal-glandular  layer.  These 
are  the  peptic  glands,  which  supply  the  most  important 
digestive  fluid — the  gastric  juice.  At  the  lower  extremity 
of  the  pouch  of  the  stomach  a  valve  develops,  which,  as 
the  pylorus,  separates  the  stomach  from  the  small  intestine 
(Fig.  275,  d). 

The  disproportionately  long  middle  intestine,  or  small 
intestine,  now  develops  below  the  stomach.  The  develop- 
ment of  this  section  is  very  simple,  and  is  essentially  caused 
by  a  very  rapid  and  considerable  longitudinal  growth. 
Originally  this  section  is  very  short,  straight,  and  simple ; 
but  immediately  below  the  stomach  a  horseshoe  bend,  or 
loop,  begins  to  appear  at  a  very  early  period  in  the  intestinal 
canal,  simultaneously  with  the  separation  of  the  intestinal 
tube  from  the  yelk-sac  and  with  the  development  of  the 
mesentery.  (Cf.  Plate  V.  Fig.  14,  g,  and  Fig.  136,  vol.  i.  p.  381.) 
Before  the  abdominal  wall  closes,  a  horseshoe-shaped  loop  of 
intestine  (Fig.  136,  m)  protrudes  from  the  ventral  opening  of 
the  embryo,  and  into  the  curve  of  this  the  yelk-sac  or  navel- 
bladder  opens  (n).  The  thin,  delicate  membrane  which 
secures  this  intestinal  loop  to  the  ventral  side  of  the  vertebral 
column,  and  occupies  the  inside  of  this  horseshoe  curve,  is 
the  first  rudiment  of  the  mesentery  (Fig.  286,  g).  The  most 
prominent  part  of  the  loop  into  which  the  yelk-sac  opens 
(Fig.  287,  x),  and  which  is  afterwards  closed  by  the  intestinal 
navel,  represents  that  part  of  the  small  intestine  which  is 
afterwards  called  the  crooked  intestine  (ileum).  Soon  a 
very  considerable  growth  of  the  small  intestine  is  observ- 
able ;  and  in  consequence,  this  part  has  to  coil  itself  in  many 
loops.     The  various  parts  of  the  small  intestine  which  we 


THE   SMALL   INTESTINE.  34 1 

have  yet  to  distinguish  differentiate  later  in  a  very  simple 
way;  these  are  the  gall-intestine  (duodenum),  which  is 
next  to  the  stomach,  the  long  empty  intestine  (jejunum) 
which  succeeds,  and  the  last  section  of  the  small  intestine, 
the  crooked  intestine  (ileum). 

The  two  large  glands  which  we  have  already  named,  the 
liver  and  the  ventral  salivary  gland,  grow  out,  as  protuber- 
ances, from  the  gall-intestine,  or  duodenum.  The  liver  first 
appears  in  the  form  of  two  small  sacs,  situated  right  and  left 
just  behind  the  stomach  (Figs.  284,/,  285,  c).  In  many  low 
Vertebrates  the  two  livers  remain  quite  separate  for  a  long- 
time (in  the  Myxinoides  for  life),  and  coalesce  only  imper- 
fectly. In  higher  Vertebrates,  on  the  other  hand,  the  two 
livers  coalesce  more  or  less  completely  at  an  early  period, 
and  constitute  one  large  organ.  The  intestinal-glandular 
layer,  which  lines  the  hollow,  pouch-like  rudiment  of  the 
liver,  sends  a  number  of  branched  processes  into  the  investing 
intestinal-fibrous  layer ;  as  these  solid  processes  (rows  of 
gland-cells)  again  branch  out,  and  as  their  branches  coalesce, 
the  peculiar  netted  structure  of  the  developed  liver  is 
produced.  The  liver-cells,  as  the  secreting  organs  which 
form  the  bile,  all  originate  from  the  intestinal-glandular 
layer.  The  fibrous  mass  of  connective  tissue,  which  joins 
this  great  cellular  network  into  a  large  compact  organ,  and 
which  invests  the  whole,  comes,  on  the  other  hand,  from  the 
intestinal-fibrous  layer.  From  the  latter  originate  also  the 
great  blood-vessels  which  traverse  the  entire  liver,  and 
the  innumerable  netted  branches  of  which  are  interlaced 
with  the  network  of  the  liver-cells.  The  gall-ducts,  which 
traverse  the  entire  liver,  collecting  the  bile  and  discharging 
it  into  the  intestine,  originate  as  intercellular  passages  along 


342 


THE   EVOLUTION   OF  MAN. 


the  axis  of  the  solid  cell-cords ;  they  all  discharge  into  the 
two  primitive  main  gall  or  biliary  ducts,  which  originate 
from  the  base  of  the  two  original  protuberances  of  the 
intestine.  In  Man,  and  in  many  other  Vertebrates,  these 
two  ducts  afterwards  unite,  and  form  one  simple  gall-duct, 
which  discharges  into  the  ascending  portion  of  the  gall- 
intestine.  The  gall  bladder  originates  as  a  hollow  pro- 
tuberance of  the  right  primitive  liver  duct.  The  growth 
of  the  liver  is  at  first  exceedingly  rapid ;  in  the  human 
embryo,  even  in  the  second  month,  it  attains  such  dimen- 
sions that  during  the  third  month  it  occupies  by  far  the 
largest  part  of  the  body-cavity  (Fig.  288).     At  first,  both 


Fig.  288.— Chest  and  abdominal  viscera  of  a 
human  embryo  of  twelve  weeks,  in  natural  size. 
(After  Koelliker.)  The  head  is  omitted ;  the  chest 
and  abdominal  walls  removed.  The  greater  part 
of  the  abdominal  cavity  is  occupied  by  the  liver, 
from  an  opening  in  the  centre  of  which  the  blind- 
intestine  (coscum,  v),  with  the  worm  appendage, 
protrudes.  Above  the  diaphragm  the  heart  is 
visible  in  the  centre,  with  the  small  lungs  on  the 
right  and  left. 


halves  are  equally  well  developed ;  afterwards  the  left  half 
lies  considerably  behind  the  right.  In  consequence  of  the 
asymmetrical  development  and  alteration  in  the  position  of 
the  stomach  and  other  abdominal  viscera,  the  whole  of  the 
liver  is  eventually  forced  over  on  to  the  right  side.  Although 
the  growth  of  the  liver  is,  afterwards,  not  so  excessive,  even 
at  the  end  of  gestation,  it  is  comparatively  much  larger  in 
the  embryo  than  in  the  adult.     In  the  latter,  its  weight 


THE   LARGE  INTESTINE. 


343 


in  proportion  to  that  of  the  whole  body  is  as  1 :  36 ;  in  the 
former,  as  1 :  18.  The  physiological  significance  of  the  liver 
•  luring  embryonic  life— which  is  very  great— depends  espe- 
cially on  the  part  it  plays  in  the  formation  of  blood,  and 
less  on  its  secretion  of  bile. 

From  the  gall-intestine,  immediately  behind  the  liver, 
grows  another  large  intestinal  gland,  the  ventral -salivary 
gland,  or  pancreas.  This  organ,  which  occurs  only  in 
Skulled  Animals,  also  develops  as  a  hollow  sac-shaped 
protuberance  of  the  intestinal  wall.  The  intestinal-glan- 
dular layer  of  the  latter  sends  out  branching  shoots,  which 
afterwards  become  hollow.  The  ventral-salivary  gland,  just 
like  the  salivary  glands  of  the  mouth,  develops  into  a  large 
and  very  complex  gland  shaped  like  a  bunch  of  grapes. 
The  outlet  of  this  gland  (ductus  pancreaticus),  through 
which  the  pancreatic  juice  passes  into  the  gall-intestine, 
seems  to  be  at  first  simple  and  single;  afterwards  it  is 
often  double. 

The  last  section  of  the  intestinal  tube,  the  terminal 
intestine  or  large  intestine  (epigaster),  in  mammalian 
embryos,  is,  at  first,  a  very  simple,  short,  and  straight  tube, 
opening  posteriorly  through  the  anus.  In  the  lower  Ver- 
tebrates it  retains  this  form  throughout  life.  In  Mammals, 
on  the  other  hand,  it  grows  to  a  considerable  size,  coils,  and 
differentiates  into  different  sections,  of  which  the  foremost 
and  longest  is  called  the  colon,  the  shorter  and  hinder  the 
rectum.  At  the  commencement  of  the  former  a  valve 
(yalvula  Bauhvai)  forms,  which  divides  the  large  intestine 
from  the  small  intestine;  behind  appears  a  pouch-like 
protuberance,  which  grows  larger  and  becomes  the  Mind- 
intestine  (cceewn)  (Fig.  288,  v).  In  plant-eating  Mammals 
38 


344  THE   EVOLUTION    OF   MAN. 

this  becomes  very  large,  while  in  those  which  eat  flesh  it 
remains  very  small,  or  is  entirely  aborted.  In  Man,  as  in 
most  Apes,  the  beginning  of  the  blind  intestine  alone 
becomes  wide  ;  its  blind  end  remains  very  narrow,  and 
afterwards  appears  only  as  a  useless  appendage  of  the 
former.  This  "  vermal  appendage "  is  interesting  in  dys- 
teleology  as  a  rudimentary  organ.  Its  only  importance  in 
Man  consists  in  the  fact  that  now  and  then  a  raisin-stone, 
or  some  other  hard,  indigestible  particle  of  food  becomes 
lodged  in  its  narrow  cavity,  causing  inflammation  and 
suppuration,  and,  consequently,  killing  individuals  other- 
wise perfectly  healthy.  In  our  plant-eating  ancestors  this 
rudimentary  organ  was  larger,  and  was  of  physiological 
value. 

Finally,  we  must  mention  another  important  appendage 
of  the  intestinal  tube;  this  is  the  urinary  bladder  (uro- 
cystis)  with  the  urinary  tube  (urethra),  which  in  develop- 
ment and  in  morphological  character  belong  to  the  intestinal 
system.  These  urinary  organs,  which  act  as  receptacles  and 
excretory  passages  for  the  urine  secreted  by  the  kidneys, 
originate  from  the  inner  part  of  the  allantois-stalk.  The 
allantois  develops,  as  a  sac-like  protuberance,  from  the 
anterior  wall  of  the  last  section  of  the  intestine  (Fig.  286,  u). 
In  the  Dipneusta  and  Amphibia,  in  which  this  blind-sac 
first  appears,  it  remains  within  the  body-cavity  (cceioma), 
and  acts  entirely  as  a  urinary  bladder.  In  all  Amniota,  on 
the  other  hand,  it  protrudes  considerably  out  of  the  body- 
cavity  of  the  embryo,  and  forms  the  large  embryonic 
"  primitive  urinary  sac,"  which,  in  higher  Mammals,  forms 
the  placenta.  At  birth  this  is  lost ;  but  the  long  allantois- 
stalk  (r)  remains,  its  upper  portion  forming  the  central  navel 


THE   URINARY  BLADDER.  345 

band  of  the  urinary  vesicle  (ligamentum  vesico-umbilicale 
medium),  a  rudimentary  organ  which  extends  as  a  solid 
cord  from  the  top  of  the  urinary  bladder  to  the  navel.  The 
lower  part  of  the  allantois-pedicle  (the  "  urachus  ")  remains 
hollow,  and  forms  the  urinary  bladder.  At  first,  in  Man, 
as  in  the  lower  Vertebrates,  this  organ  discharges  into  the 
last  section  of  the  posterior  intestine,  and  there  is,  there- 
fore, a  true  "  cloaca,"  receiving  both  urine  and  excrement ; 
but,  among  the  Mammals,  this  cloaca  is  permanent  only  in 
the  Cloacal  Animals,  or  Monotremes,  as  in  Birds,  Reptiles, 
and  Amphibia.  In  all  other  Mammals  (Marsupialia  and 
Placentiilia)  a  transverse  partition  forms  at  a  later  period, 
and  separates  the  urinary-sexual  aperture  in  front  from  the 
anal  aperture  behind.     (Cf.  Chapter  XXV.) 


(    346    ) 


EXPLANATION  OF  PLATE  I.— (Frontispiece.) 

Development  of  the  Face. 

The  twelve  figures  in  Plate  I.  represent  the  faces  of  four  different 
Mammals  in  three  distinct  stages  of  individual  evolution  :  Mi-Miii  that  of 
Man,  Br-Bin  of  the  Bat,  Ci-Ciii  of  the  Cat,  Si-Sin  of  the  Sheep.  The 
three  different  stages  of  evolution  have  heen  chosen  to  correspond  as  far  as 
possible  ;  they  have  been  reduced  to  about  the  same  size,  and  are  seen  from 
iu  front.  In  all  the  figures  the  letters  indicate  the  same :  a,  eye  ;  v,  fore- 
brain  ;  m,  mid-brain  ;  s,  frontal  process  ;  k,  nose-roof  ;  o,  upper  jaw  process 
(of  the  first  gill-arch)  ;  w,  lower  jaw  process  (of  the  first  gill-arch)  ;  h, 
second  gill-arch ;  d,  third  gill-arch ;  r,  fourth  gill-arch ;  g,  ear-fissure 
(remains  of  the  front  gill-opening) ;  z,  tongue.  (Cf .  Plates  VI.  and  VII., 
Figs.  232-236,  p.  2 13 ;  also  Figs.  123,  124,  vol.  i.  p.  370.) 


TABLE    XXXVII. 

Systematic  Survey  of  the  most  Important  Periods  in  tiie 
Phylogeny  of  the  Human  Intestinal  System. 

I.  First  Period:  Intestine  of  Gastrcea  (Figs.  274-277;   Plate  V.  Figs.  9,  10). 
The  whole  intestinal  system  is  a  simple  pouch  (primitive  intestine),  the 
simple  cavity  of  which  has  one  orifice  (the  primitive  mouth). 

II.  Second  Period  :  Intestine  of  the  Scolecida  (Plate  V.  Fig.  11). 
The  simple  intestinal  tube  widens  in  the  middle  into  the  stomach,  and 
acquires,  at  the  end  opposite   to   the  primitive  mouth,  a  second  opening 
(primitive  anus) ;  as  in  the  lower  Worms. 

III.   Third  Period  :  Intestine  of  Chorda  Animals  (Fig.  281;  Plate  V.  Fig.  12). 

The  intestinal  tube  differentiates  into  two  main  sections — the  respiratory 

intestine  with  gill-openings  (gill-intestine)   in  front,  the  digestive  intestine 

with  stomach-cavity  (stomach-intestine)  behind  ;  as  in  Ascidia. 


SURVEY   OF   HUMAN    INTESTINAL   SYSTEM.  T>47 

IV.  Fourth  Period  :  Intestine  of  Skull-less  Animals  (Acrania) 
(Fig.  282;  Plate  XI.  Fig.  15). 
The  gill-streaks  appear   between    the  gill-openings    of    the    respiratory 
intestine  ;  a  liver  blind-sac  grows  from  the  stomach-pouch  of  the  digestive 
intestine  ;  as  in  the  Amphioxus. 

V.  Fifth  Period:  Intestine  of  Cyclostoma  (Plate  XI.  Fig.  1G). 
The   thyroid   gland    develops    from    the  ciliated  groove  on  the  base  of 
the  gills   (liypobianchial    groove).       A  compact    liver-gland    develops  from 
the  liver  blind-sac. 

VI.  Sixth  Period:  Intestine  of  Primitive  Fishes  (p.  111). 
Cartilaginous  gill-arches  appear  between  the  gill-openings.      The  fore- 
most of  these  form  the  lip-cartilages  and  the  jaw-skeleton  (upper  and  lower 
jaw).     The  swimming-bladder  grows  from  the  pharynx.     The  ventral-salivary 
gland  appears  near  the  liver,  as  in  Selachii. 

VII.  Seventh  Period  :  Intestine  of  Dipneusta  (p.  118). 

The  swimming-bladder  modifies  into  the  lungs.  The  mouth-cavity 
becomes  connected  with  the  nose-cavity.  The  urinary  bladder  grows  from 
the  last  section  of  the  intestine,  as  in  Lepidosiren. 

VIII.  Eighth  Period:  Intestine  of  Amphibia  (p.  12G). 

The  gill-openings  close.  The  gills  are  lost.  The  larynx  originates  from 
the  upper  end  of  the  trachea. 

IX.  Ninth  Period:  Intestine  of  Monotremes  (p.  145). 
The  primitive  mouth  and  nasal   cavity  is   separated  by  the  horizontal 
palate-roof  into  the  lower  mouth-cavity  (food  passage)  and  the  upper  nose- 
cavity  (air  passage);  as  in  all  Amnion  Animals. 

X.   Tenth  Period:  Intestine  of  Marsvpials  (p.  149). 
The  existing  cloaca  is  separated    by  a  partition  wall  into  an  anterior 
urinary-sexual  aperture  and  a  posterior  anal  aperture. 

XT.  Eleventh  Period:   Intestine  of  Catarhine  Apes  (p.  17G). 
All  parts  of  the  intestine,  and  especially  the  teeth-apparatus,  acquire  the 

characteristic  development  common  to  Man  and  Catarhine  Apes. 


CHAPTER  XXIV. 

DEVELOPMENT   OF   THE   VASCULAR   SYSTEM. 

Application  of  the  Fundamental  Law  of  Biogeny. — The  Two  Sides. — Heredity 
of  Conservative  Organs. — Adaptation  of  Progressive  Organs. — Ontogeny 
and  Comparative  Anatomy  complementary  of  each  other. — New 
"Theories  of  Evolution"  of  His. — The  "Envelope  Theory"  and  the 
"  Waste-rag  Theory." — Main  Germ  and  Supplementary  Germ. — Forma- 
tive Yelk  and  Nutritive  Yelk. — Phylogenetic  Origin  of  the  latter  from 
the  Primitive  Intestine.— Origin  of  the  Vascular  System  from  the 
Vascular  Layer,  or  Intestinal-fibrous  Layer. — Phylogenetic  Significance 
of  the  Ontogenetic  Succession  of  the  Organ-systems  and  Tissues. — 
Deviation  from  the  Original  Sequence;  Ontogenetic  Heterochronism. — 
Covering  Tissue. — Connective  Tissue. — Nerve-muscle  Tissue. — Vascular 
Tissue. — Relative  Age  of  the  Vascular  System. — First  Commencement 
of  the  Latter;  Coeloma. — Dorsal  Vessel  and  Ventral  Vessel  of  Worms. 
— Simple  Heart  of  Ascidia. — Atrophy  of  the  Heart  in  the  Amphioxus. — ■ 
Two-chambered  Heart  of  the  Cyclostoma. — Arterial  Arches  of  the 
Selachii.- — Double  Auricle  in  Dipneusta  and  Amphibia. — Double  Ven- 
tricle in  Birds  and  Mammals. — Arterial  Arches  in  Birds  and  Mammals. 
Germ-history  (Ontogeny)  of  the  Human  Heart. — Parallelism  of  the 
Tribal-history  (Phylogcny). 

"  Morphological  comparison  of  the  adult  conditions  should  naturally 
precede  the  study  of  the  earliest  conditions.  Only  in  this  way  can  the 
investigation  of  the  history  of  development  proceed  in  a  definite  direction ; 
it  is  thus  provided,  as  it  were,  to  see  each  step  in  the  formative  process  in 
its  true  relation  with  the  condition  which  is  finally  to  be  reached.  Treat- 
ment of  the  history  of  development  without  preparatory  study  is  only  too 


APPLICATION  OF   THE  LAW   OF  BIOGENY.  349 

likely  to  lead  to  groping  in  the  dark ;  and  it  not  unfrequently  lea'ls  to  the 
most  unfortunate  results— far  inferior  to  those  which  might  be  established 
beyond  question  without  any  study  of  the  history  of  development."— 
Alexander  Buaun  (1872). 

In  applying  to  Organogeny  the  fundamental  law  of  Bio- 
o-eny,  we  have  already  afforded  some  conception  of  the 
decree  in  which  we  may  follow  its  guidance  in  the  study  of 
tribal  history.  The  degree  differs  greatly  in  the  different 
organ-systems  ;  this  is  so,  because  the  capacity  for  trans- 
mission on  one  side,  and  the  capacity  for  modification  on 
the  other,  vary  greatly  in  the  different  organs.  Some  parts 
of  the  body  cling  tenaciously  to  the  inherited  germ-history ; 
and,  owing  to  heredity,  accurately  retain  the  mode  of 
evolution  inherited  from  primaeval  animal  ancestors  ;  other 
parts  of  the  body,  on  the  contrary,  exhibit  very  small 
capacity  for  strict  heredity,  and  have  a  great  tendency  to 
assume  new  kenogenetic  forms  by  adaptation,  and  to  modify 
the  original  Ontogeny.  The  former  organs  represent,  in  the 
many-celled  community  of  the  human  organism,  the  con- 
stant or  conservative;  the  latter,  on  the  contrary,  the 
changeable  or  progressive  element  of  evolution.  The  mutual 
interaction  of  both  elements  determines  the  course  of  his- 
torical evolution. 

Only  to  the  conservative  organs,  in  which  Heredity  pre- 
ponderates over  Adaptation,  in  the  course  of  tribal  evolu- 
tion, can  we  directly  apply  the  Ontogeny  to  the  Phylogeny, 
and  can  infer,  from  the  palingenetic  modification  of  the 
germ-forms,  the  primaeval  metamorphosis  of  the  tribal  forms. 
In  the  progressive  organs,  on  the  contrary,  in  which  Adap- 
tation has  acquired  the  ascendency  over  Heredity,  the 
original  course  of  evolution  has,  usual ly,  been  so  changed, 


350  THE   EVOLUTION   OF   MAN. 

vitiated,  and  abbreviated,  in  the  course  of  time,  that  we 
can  gain  but  little  certain  information  as  to  the  tribal- 
history  from  the  kenogenetic  phenomena  of  their  germ- 
history.  Here,  therefore,  Comparative  Anatomy  must  come 
to  our  help,  and  it  often  affords  much  more  important  and 
trustworthy  disclosures  as  to  Phylogeny  than  Ontogeny 
is  able  to  impart.  It  is,  therefore,  most  important,  if  the 
fundamental  law  of  Biogeny  is  to  be  correctly  and  critically 
applied,  to  keep  its  two  sides  continually  in  view.  The 
first  half  of  this  fundamental  law  of  evolution  enables  us  to 
use  Phylogeny,  as  it  shows  us  how  to  gain  an  approximate 
knowledge  of  the  history  of  the  tribe  from  that  of  the 
germ :  the  germ-form  reproduces,  by  Heredity,  the  corre- 
sponding tribal  form  (Palingenesis).  The  other  half  of 
the  law,  however,  limits  this  guiding  principle,  and  calls 
attention  to  the  foresight  with  which  it  must  be  employed  ; 
it  shows  us  that  the  original  reproduction  of  the  Phylogeny 
in  the  Ontogeny  has  been  in  many"  ways  altered,  vitiated, 
and  abbreviated,  in  the  course  of  millions  of  years.  The 
germ-form  has  deviated,  by  Adaptation,  from  the  corre- 
sponding tribal  form  (Kenogenesis) ;  the  greater  this  devia- 
tion, the  more  are  we  compelled  to  employ  Comparative 
Anatomy  in  the  study  of  Phylogeny. 

Perhaps  in  no  other  system  of  organs  of  the  human  bod}- 
is  this  so  greatly  the  case  as  in  the  vascular  system  (vas- 
cular, or  circulatory  apparatus),  the  development  of  which 
we  will  now  examine.  If  we  attempted  to  infer  the 
original  structural  features  of  our  older  animal  ancestors 
solely  from  the  phenomena  which  the  individual  develop- 
ment of  these  organ-systems,  in  the  embryo  of  Man  and  of 
other  high  Vertebrates,  exhibit,  we  should  obtain  wholly 


HIS  ON  THE  VASCULAR  SYSTEM.  35  I 

erroneous  views.  By  many  influential  embryonic  adap- 
tations, among  which  the  development  of  an  extensive 
nutritive  }7elk  must  be  regarded  as  the  most  important,  the 
original  course  of  development  of  the  vascular  system  has 
been  so  altered,  vitiated,  and  abbreviated,  in  the  higher 
Vertebrates,  that  no,  or  very  little,  trace  of  many  of  the 
most  important  phylogenetic  features  are  retained  in  the 
Ontogeny.  Such  explanation  as  is  afforded  by  the  latter 
would  be  entirely  useless  to  us  if  Comparative  Anatomy 
did  not  lend  its  aid,  and  afford  us  the  clearest  guidance  in 
our  search  for  tribal  history. 

Comparative  Anatomy  is,  therefore,  especially  important 
in  helping  us  to  understand  the  vascular  system,  and, 
equally,  the  skeleton  system,  so  that,  without  its  guidance, 
it  is  unsafe  to  take  a  single  step  in  this  diflicult  field. 
Positive  proof  of  this  assertion  can  be  gained  by  studying 
the  complex  vascular  system  as  explained  in  the  classical 
works  of  Johannes  Muller,  Heinrich  Rathke,  and  Karl 
Gegenbaur.  An  equally  strong  negative  proof  of  the  asser- 
tion is  afforded  by  the  ontogenetic  works  of  Wilhelm  His, 
an  embryologist  of  Leipsic,  who  has  no  conception  of  Com- 
parative Anatomy,  nor  consequently,  of  Phylogeny.  In 
18G8,  this  industrious  but  uncritical  worker  published  cer- 
tain comprehensive  "  Studies  of  the  First  Rudiment  of  the 
Vertebrate  Body,"  which  are  among  the  most  wonderful 
pioductions  in  the  entire  literature  of  Ontogeny.  As  the 
author  hopes  to  attain  a  "mechanical"  theory  of  develop- 
ment by  means  of  a  most  minute  description  of  the  germ- 
history  of  the  Chick  alone,  without  the  slightest  reference 
to  Comparative  Anatomy  and  Phylogeny,  he  falls  into 
errors  which  are  unparalleled   in    the  whole  literature    of 


352  THE   EVOLUTION    OF   MAN. 

Biology,  rich  as  this  unfortunately  is  in  errors.  Only  in  the 
magnificent  germ-history  of  the  Bombinator  by  Alexander 
Goette  is  incomprehensible  nonsense  and  derision  of  every 
reasonable  causal  connection  in  evolution  more  nakedly  set 
forth.  (Cf.  vol.  i.  pp.  65,  6Q.)  His  announces,  as  the  final 
result  of  his  investigations,  "  that  a  comparatively  simple 
law  of  growth  is  the  only  essential  in  the  first  process  of 
evolution.  All  formation,  whether  it  consist  in  fission  of 
layers,  or  in  the  formation  of  folds,  or  in  complete  articula- 
tion, results  from  this  fundamental  law."  Unfortunately 
the  author  does  not  say  in  what  this  all-embracing  "  law  of 
growth"  really  consists;  just  like  other  opponents  of  the 
theory  of  descent  who  substitute  a  great  "law  of  evolution," 
without  telling  anything  of  its  nature.  From  the  study  of 
the  ontogenetic  works  of  His,  on  the  of.  er  hand,  it  soon 
becomes  evident  that  he  conceives  form-constructing; 
"  Mother  Nature  "  merely  as  a  kind  of  clever  dressmaker ; 
by  cutting  out  the  germ-layers  in  various  ways,  by  bend- 
ing, folding,  pulling,  and  splitting  them,  this  clever  semp- 
stress easily  brings  into  existence  the  various  forms  of 
animal  species,  by  "  development "  (!).  The  bendings  and 
foldings  especially  play  the  most  important  part.  Not  only 
the  differentiation  of  head  and  trunk,  of  right  and  left,  of 
central  stem  and  periphery,  but  also  the  rudiment  of  the 
limbs,  as  also  the  articulation  of  the  brain,  the  sense-organs, 
the  primitive  vertebral  column,  the  heart,  and  the  earliest 
intestines,  can  be  shown,  with  convincing  necessity  (!)  to  be 
mechanical  results  of  the  first  development  of  folds.  Most 
grotesque  is  the  mode  in  which  the  dressmaker  proceeds  in 
forming  the  two  pairs  of  limbs.  Their  first  form  is  deter- 
mined by  the  crossing  of  four  folds  bordering  the  body, 


HIS  ON  THE   VASCULAR  SYSTEM.  353 

"  like  the  four  corners  of  a  letter."  Yet  this  wonderful 
"  envelope  theory  "  of  the  vertebrate  limbs  is  surpassed  by 
the  *  waste-rag  theory  "  (Hollen-lappen  Theorie)  which  His 
gives  of  the  origin  of  the  rudimentary  organs :  "  Organs 
(like  the  hypophysis  and  the  thyroid  gland)  to  which  no 
physiological  part  has  yet  been  assigned,  are  embryonic 
remnants,  comparable  to  the  clippings,  which  in  the  cutting 
of  a  dress  cannot  be  entirely  avoided,  even  by  the  most 
economical  use  of  the  material  "  (!).  Nature,  therefore,  in 
cutting  out,  throws  the  superfluous  rags  of  tissue  into  the 
waste  heap.  Had  our  skull-less  ancestors  of  the  Silurian 
age  had  any  presentiment  of  such  aberrations  of  intellect 
of  their  too  speculative  human  descendants,  they  would 
certainly  have  preferred  relinquishing  possession  of  the 
hypobranchial  groove  on  the  gill-body,  instead  of  trans- 
mitting it  to  the  extant  Amphioxus,  and  of  leaving  a 
remnant  of  it  to  us,  in  the  equally  unsightly  as  useless 
thyroid  gland.     (Cf.  p.  336). 

It  will  probably  be  thought  that  the  ontogenetic  "dis- 
coveries" of  His,  which  appear  in  a  doubly  comical  light  in 
consequence  of  the  accompanying  display  of  mathematical 
calculations,  can  only  have  occasioned  momentary  amuse- 
ment in  critical  scientific  circles.  Far  from  it !  Immedi- 
ately after  their  appearance,  they  were  not  only  much 
praised  as  the  beginning  of  a  new  "  mechanical "  era  in 
Ontogeny,  but  they  have  even  yet  numerous  admirers  and 
adherents,  who  seek  to  spread  the  scientific  errors  of  His  as 
far  as  possible.  On  this  account,  I  have  felt  myself  obliged 
to  point  out  emphatically  the  complete  falsity  of  these 
views,  The  vascular  system  affords  especial  occasion  for 
this  ;  for  among  the  most  important  advances  which  His 


354  THE   EVOLUTION   OF   MAN. 

claims  to  have  caused  by  his  new  conception  of  germ- 
history,  is,  according  to  him,  his  discovery  that  "  the  blood 
and  tissue  of  the  connective  substance  "  (that  is  to  say,  the 
greatest  part  of  the  vascular  system)  "  do  not  originate  from 
the  two  primary  germ-layers,  as  do  all  the  other  organs, 
but  from  the  elements  of  the  white  yelk."  The  latter 
is  designated  as  "  supplementary  yelk,  or  parablast,"  to 
distinguish  it  from  the  "main-germ,  or  archiblast"  (the 
germ- disc  composed  of  the  two  primary  germ-la}-ers). 

The  whole  of  this  artificial  development  theory  of  His, 
and  above  all  the  unnatural  distinction  between  the  supple- 
mentary and  the  main  germ,  collapses  like  a  card  house 
when  the  Anatomy  and  Ontogeny  of  the  Amphioxus,  that 
invaluable  lowest  Vertebrate,  is  contemplated,  which  alone 
can  elucidate  the  most  difficult  and  darkest  features  in  the 
development  of  the  higher  Vertebrates,  and  thus  also  of 
Man.  The  gastrula  of  the  Amphioxus  alone  overthrows 
the  whole  artificial  theory ;  for  this  gastrula  teaches  us 
that  all  the  various  organs  and  tissues  of  complete  Verte- 
brates originally  developed  entirely  from  the  two  primary 
germ-layers.  The  developed  Amphioxus,  like  all  other 
Vertebrates,  has  a  differentiated  vascular  system  and 
a  skeleton  of  "  connective  substance  tissues "  extending 
throughout  its  body,  and  yet  there  is  in  this  case  no  "  sup- 
plementary germ "  from  which  these  tissues  can  originate 
thus,  contrasting  with  the  other  tissues. 

The  larvse  of  the  Amphioxus,  arising  from  the  original 
bell-gastrula  (archi  gastrula),  in  its  further  development, 
throws  the  most  important  rays  of  light  also  upon  the  diffi- 
cult history  of  development  of  the  vascular  system.  In  the 
first  place,  it  answers  the  very  important  question,  which 


THE  VASCULAR  SYSTEM.  355 

we  have  already  frequently  indicated,  as  to  the  origin  of 
the  four  secondary  germ-layers ;  it  clearly  shows  that  the 
skin-fibrous  layer  originates  from  the  exoderm,  the  intes- 
tinal-fibrous layer,  on  the  contrary,  in  an  analogous  manner, 
from  the  entoderm  of  the  gastrula ;  the  cavity  thus  caused 
between  the  two  fibrous  layers  is  the  first  rudiment  of  the 
body-cavity,  or  the  ccelom  (Figs.  50,  51,  vol.  i.  p.  236).  .  As  the 
Amphioxus  larva  thus  shows  that  the  fission  of  the  layers 
is  the  same  in  the  lowest  Vertebrates  as  in  the  Worms,  it  at 
the  same  time  represents  the  phylogenetic  connection  be- 
tween the  Worms  and  the  higher  Vertebrates.  As,  more- 
over, the  primitive  vascular  stems  in  the  Amphioxus 
originate  in  the  intestinal  wall,  and  in  this,  as  in  the  em- 
bryos  of  all  other  Vertebrates,  proceed  from  the  intestinal- 
fibrous  la}Ter,  proof  is  afforded  us  that  the  earlier  embryolo- 
gists  were  right  in  calling  the  latter  the  vascular  layer. 
Finally,  the  Comparative  Ontogeny  of  the  different  verte- 
brate classes  further  convinces  us  that  the  vascular  layer 
is  originally  everywhere  the  same.  The  vascular  system  in 
Man,  as  in  all  Skulled  Animals,  forms  a  complex  apparatus 
of  cavities,  which  are  filled  with  juices,  or  fluids,  containing 
cells.  The  vessels  play  an  important  part  in  the  nourish- 
ment of  the  body  ;  some  of  them  conduct  the  nutritive 
blood  fluid  round  in  the  different  parts  of  the  body  (blood- 
vessels) ;  some  collect  the  wasted  juices  and  discharge  them 
from  the  tissues  (lymph-vessels).  With  the  latter,  the 
great  "serous  cavities"  are  also  connected,  especially  the 
body-cavity,  or  cceloma.  The  heart,  acting  as  a  centre  of 
motion  for  the  regular  circulation  of  the  juices,  is  a  strong 
muscular  pouch,  which  contracts  in  regular  pulsations,  and 
is  provided  with  valves,  like  those  of  a  pump  apparatus 


356  THE   EVOLUTION    OF   MAN. 

This  constant  and  regular  circulation  of  the  blood  alone 
makes  the  complex  change  of  substance  with  the  higher 
animals  possible. 

Important  as  is  the  vascular  system  in  the  more  highly 
developed  and  differentiated  animal  body,  it  is  not,  however, 
an  apparatus  as  indispensable  to  animal  life  as  is  generally 
supposed.  In  the  older  theory  of  medicine  the  blood  was 
regarded  as  the  real  source  of  life,  and  "  humoral  pathology" 
referred  most  diseases  to  "  corrupt  blood-mixture."  Simi-. 
larly,  the  blood  plays  the  most  important  part  in  the  pre- 
vailing, obscure  conception  of  Heredity.  Just  as  half-blood, 
pure  blood,  etc.,  etc.,  are  yet  common  phrases,  so  it  is  widely 
believed  that  the  transmission,  by  Heredity,  of  definite 
morphological  and  physiological  characters  from  the  parent 
to  the  child  "lies  in  the  blood."  That  this  customary 
notion  is  entirely  false,  is  easily  seen  from  the  fact  that, 
neither  in  the  act  of  procreation  is  the  blood  of  the  parents 
directly  transmitted  to  the  procreated  germ,  nor  does  the 
embryo  acquire  blood  at  an  early  period.  As  we  have 
already  seen,  not  only  the  separation  of  the  four  secondary 
germ-layers,  but  also  the  beginning  of  the  most  impor- 
tant organs,  takes  place,  in  the  embryos  of  all  Vertebrates, 
before  the  rudiment  of  the  vascular  systems,  of  the  heart 
and  blood,  is  formed.  In  accordance  with  this  ontogenetic 
fact,  we  must,  from  a  phylogenetic  point  of  view,  regard  the 
vascular  system  as  the  most  recent,  the  intestinal  system, 
on  the  contrary,  as  the  oldest  formation  of  the  animal  body. 
The  origin  of  the  vascular  system  is,  at  least,  much  later 
than  that  of  the  intestinal  system.  If  the  fundamental  law 
of  Biogeny  is  rightly  appreciated,  it  is  possible,  from  the 
ontogenetic  sequence,  in  which   the   various   organs  of  the 


AGE   OF   THE   VASCULAR   SYSTEM.  357 

animal  body  consecutively  originate  in  the  embryo,  approxi- 
mately to  infer  the  phylogenetic  sequence,  in  which  these 
organs  gradually  developed,  one  after  the  other,  in  the 
ancestral  line  of  animals.  In  the  "  Gastrrea  theory  "  I  made 
the  first  attempt  to  establish  the  phylogenetic  significance 
of  the  ontogenetic  sequence  of  the  organ-systems;  but  it 
must  be  remarked  that  this  sequence  is  not  always  iden- 
tical in  the  higher  animal  tribes.  In  Vertebrates,  and 
therefore  also  in  our  own  ancestral  line,  the  organ-systems 
may  be  ranged  according  to  age,  in  something  like  the 
following  order :  I.  The  skin-system  (A)  and  the  intestinal 
system  (B).  II.  The  nerve  (C)  and  muscular  systems  (D). 
III.  The  kidney  system  (E).  IV.  The  vascular  system  (F). 
V.  The  skeleton  system  (G).  VI.  The  sexual  system  (//). 
(Cf.  Table  XXXIX,  p.  3G7.) 

In  the  first  place,  the  gastrula  proves  that  in  all  animals 
with  the  exception  of  the  Primitive  Animals  {Protozoa), — 
therefore,  in  all  Intestinal  Animals  (Metazoa), — two  primary 
organ-systems  originally  arose  simultaneously  and  first; 
these  were  the  skin-system  (skin-covering)  and  the  intes- 
tinal system  (stomach-pouch).  The  first  is  represented,  in 
its  earliest  and  simplest  form,  by  the  skin-layer  or  exoderm, 
the  latter  by  the  intestinal  layer  or  entoderm  of  the  Gastrrea. 
As  we  can  ascribe  the  same  origin,  and,  therefore,  also  the 
same  morphological  significance,  to  these  two  primary  germ- 
Layers  in  all  Intestinal  Animals,  from  the  simplest  Sponge 
to  Man,  the  homology  of  these  two  layers  seems  sufficient 
proof  of  the  above  assumption. 

Immediately  after  the  differentiation  of  the  two  primary 
germ-layers,  an  inner  or  outer  skeleton  develops  in  many 
lower   animals    (e.g.,  in    Sponges,   Corals,  and   other  Plant 


353  THE   EVOLUTION    OF   MAN. 

Animals).    In  the  ancestors  of  Vertebrates,  the  development 
of  the  skeleton  did  not  take  place  till  much  later,  in  the 
Chorda  Animals    (Chordonia).     In  them,    after   the   skin- 
system  and  the  intestinal  system,  two  other  organ-systems 
simultaneously  arise ;  these  are  the  nervous  and  the  mus- 
cular systems.     The  way  in  which  these  two  organ-systems 
which  mutually   condition  each  other,  developed  simulta- 
neously and  independently,  in  reciprocal  action  and  yet  in 
opposition  to  each  other,  was  first  explained  by  Nicholaus 
Kleinenberg  in  his  excellent  monograph  on  the  Hydra,  the 
common   fresh-water   Polyp.190      In   this   interesting  little 
animal,  single  cells  of  the  skin-layer  send  fibre-shaped  pro- 
cesses inward,  which  acquire  the  power  of  contraction,  the 
capacity,  characteristic  of  the  muscles,  of  contracting  in  a 
constant  direction.     The   outer,  roundish  part  of  the  exo- 
derm  cell  remains  sensitive  and  acts  as  the  nervous  element, 
the  inner,  fibre-shaped  part  of  the  same  cell  becomes  con- 
tractile, and,  incited  to  contraction  by  the  former  part,  acts 
as   the   muscular   element   (Fig.   293).      These  remarkable 
neuro-muscular  cells  thus  still  unite  in  a  single  individual 
of  the  first  order  the  functions  of  two  organ-systems.     One 
step  further;  the  inner,  muscular  half  of  the  neuro-muscular 
cell  (Fig.  293,  m)  acquires  its  own  nucleus,  and  separates 
from  the  outer,  nervous  half  (n),  and  both  organ-systems 
have  their  independent  element  of  form.     The  fission  of  the 
muscular  skin-fibrous  layer  from  the  nervous  skin-sensory 
layer  in  embryonic  Worms  confirms  this  important  phylo- 
genetic  process  (Figs.  50,  51,  vol.  i.  p.  236). 

These  four  organ-systems,  which  have  been  mentioned, 
were  already  in  existence,  when  an  apparatus  developed, 
tertiarily,    in    the    human    ancestral   line,    which,    at   first 


THE   KIDNEYS.  359 

sight,  seems  of  subordinate  significance,  but  which  proves, 
by  its  early  appearance  in  the  animal  series  and  in  the 
embryo,  that  it  must  be  very  ancient  and,  consequently,  of 
great  physiological  and  morphological  value.  This  is  the 
urinary  apparatus,  or  kidney  system,  the  organ-system 
which  secretes  and  removes  the  useless  fluids  from  the  body. 
We  have  already  seen  how  soon  the  primitive  kidneys 
appear  in  the  embryo  of  all  Vertebrates,  long  before  any 
trace  of  the  heart  is  discoverable.  Correspondingly,  we  also 
find  a  pair  of  simple  primitive  kidney  ducts  (the  so-called 
excretory  ducts  or  lymphatic  vessels)  almost  universally 
diffused  in  the  Worm  tribe,  which  is  so  rich  in  forms.  Even 
the  lowest  classes  of  Worms,  which  have  as  yet  neither 
body-cavity  nor  vascular  system,  are  furnished  with  these 
primitive  kidneys  (Fig.  280,  nc,  p.  327).  It  was  only  in 
the  fourth  place,  after  the  kidney  system,  that  the  vascular 
system  developed  in  our  invertebrate  ancestors;  this  is 
plainly  shown  in  the  Comparative  Anatomy  of  Worms. 
The  lower  Worms  (Acodomi)  possess  no  part  of  the  vas- 
cular system,  no  body-cavity,  no  blood,  no  heart,  and  no 
vessels ;  this  is  the  case,  for  example,  in  the  comprehensive 
group  of  the  Flat  Worms  (PlathelmintJies),  the  Gliding  Worms 
(Turbellaria),  the  Sucking  Worms  (Trematoda),  and  the 
Tape  Worms.  In  the  higher  Worms,  which  are  therefore 
called  Ccelomati,  a  body-cavity  (cceloma),  filled  with  blood, 
first  begins  to  form ,  and,  side  by  side  with  this,  special 
blood-vessels  then  also  develop.  These  features  have  been 
transmitted  from  the  Ccelomati  to  the  four  higher  animal 
tribes. 

These  organ-systems  are  common  to  Vertebrates  and  to 
the    three   higher   animal  tribes,    the    Articulated  Animals 


360  THE   EVOLUTION   OF  MAN. 

(Arthropoda),  the  Soft-bodied  Animals  (Mollusca),  and  the 
Star  Animals  (Echinoderma),  and  we  may,  therefore,  infer 
that  they  have  all  acquired  these,  as  a  common  inheritance 
from  the  Ccelomati ;  but  we  now  meet  with  a  passive 
apparatus  of  movement,  the  skeleton  system,  which,  in  this 
form,  is  exclusively  peculiar  to  Vertebrates.  Only  the  very 
first  rudiment  of  this,  the  simple  notochord,  is  found  in 
Ascidia,  which  are  the  nearest  invertebrate  blood-relations 
of  "Vertebrates.  We  infer  from  this,  that  the  common 
ancestors  of  both,  the  Chorda  Animals,  did  not  branch  off 
from  the  Worms  till  a  comparatively  late  period.  The 
notochord  is,  it  is  true,  one  of  those  organs  which  appear  at 
a  very  early  period  in  the  vertebrate  embryo ;  but  this  is 
clearly  due  to  an  ontogenetic  heterochronism,  to  displace- 
ment in  time  in  the  germ-history,  that  is,  a  gradual  dis- 
arrangement in  the  original  phylogenetic  sequence,  caused 
by  embryonic  adaptation.  On  Comparative  Anatomical 
grounds  it  may  safely  be  assumed,  that  the  first  origin  of 
the  skeleton  system  did  not  precede,  but  followed  that  of 
the  kidney  system  and  of  the  vascular  system,  although 
Ontogeny  appears  to  indicate  the  contrary. 

Last  of  all  the  organ-systems,  the  sexual  system  finally 
developed,  in  the  sixth  place,  in  our  ancestors ;  of  course  it 
must  be  understood  that  this  was  last,  in  the  sense  that  the 
sexual  apparatus  acquired  the  independent  form  of  a  special 
organ-system  subsequently  to  all  the  other  organs.  The 
simplest  form,  that  of  reproductive  cells,  is  certainly  very 
ancient.  Not  only  the  lowest  Worms  and  Plant  Animals 
propagate  sexually,  but  this  was  also  probably  the  case  in 
the  common  parent-form  of  all  Metazoa,  in  the  Gastnea ; 
but  in  all  these  low  animals,  the  reproductive  cells  do  not 


AGE   OF  THE   TISSUES.  36 1 

constitute  special  sexual  organs  in  a  morphological  sense; 
they  are  rather,  as  we  shall  soon  see,  simple  component  parts 
of  other  organs. 

Like  the  organ-systems  of  the  human  body,  the  tissues, 
which  compose  these  systems,  are  of  different  ages  and  of 
varying  morphological  value.  As  we  were  justified  in 
drawing  an  inference  as  to  the  phylogenetic  sequence  in 
age  of  the  organ-systems,  from  the  ontogenetic  sequence 
in  which  they  successively  appear  in  the  embryo,  so  are 
we  justified  in  inferring  the  order  in  which  the  tissues 
originated  during  the  course  of  tribal  history,  from  the 
sequence  of  the  stages  in  germ-history.  The  result  of  this 
is  a  phylogenetic  classification  (Table  XXXVIII.)  of  the 
tissues  of  the  human  body,  similar  to  that  of  the  organs 
(Table  XXXIX.,  p.  3G7). 

The  tissues  of  the  human  body,  arising  by  division  of 
labour,  the  separation  and  the  connection  of  the  component 
cells,  may  be  distributed,  with  reference  to  their  develop- 
ment, in  the  four  following  distinct  groups  : — 1,  covering- 
tissue  (epithelium) ;  2,  connective  tissue  (connect  ivum);  3, 
nerve  and  muscular  tissue  (neuro-musculuni) ;  and  4,  vas- 
cular tissue  (vasalium).  Of  these,  in  accordance  with  the 
Gastrsea  theory,  we  must  regard  the  covering-tissue  as  the 
oldest  and  most  original  form,  as  the  actual  primary  or 
primitive  tissue ;  the  three  other  main  forms  must,  on  the 
other  hand,  be  considered  as  secondary  or  derived  forms, 
which  developed  at  a  later  period  from  the  covering-tissue  ; 
the  connecting-tissue  first,  then  the  neuro-muscular,  and 
lastly  the  vascular  tissue. 

The   oldest   and   most   original   form    of  tissue  is,  un- 
doubtedly, the   covering-tissue   (epithelium),    the   cells   of 


362 


THE    EVOLUTION    OF   MAN. 


which  are  arranged  in  a  simple  strata-like  way,  and  extend 
over  the  outer  and  inner  surface  of  the  body  as  a  protective 
and  secreting  cover.  This  is  proved  by  the  simple  fact  that 
the  formation  of  the  tissues  of  the  animal  body  begins 
with  the  formation  of  the  gastrula,  and  that  the  latter 
itself  consists  solely  of  two  simple  epithelial  strata,  of  the 
skin-layer  (Fig.  274,  e),  and  of  the  intestinal-layer  (i). 
Histologically,  the  two  primary  germ-layers  are  simple 
epithelia.  When  these,  afterwards,  separate  into  the  four 
secondary  germ-layers,  the  skin-sensory  layer  becomes  the 
outermost  of  the  external  coverings  (dermal-epithelium); 
the  intestinal-glandular  layer  becomes  the  innermost  of  the 
internal  coverings  (gastral-epithelium).  The  tissue  of  the 
outer  skin  and  of  all  its  appendages,  such  as  nails  (Fig.  289), 


Fig.  289. — Tissue  of  the  nails  (flattened  epithelium)  :  a-e,  cells  of  the 
upper  strata  ;  /,  g,  cells  of  the  lower  strata. 

Fig.  290. — Tissue  of  the  covering  of  the  small  intestine  (columnar 
epithelium)  :  a,  side  view  of  three  cells  (with  thicker,  porous  borders)  ;  i, 
surface  view  of  four  cells.     (After  Frey.) 


hairs,  skin-glands,  etc.,  arise  from  the  skin-sensory  layer. 
(Cf.  Table  XXIX.,  p.  232.)  The  inner  covering  of  the  intes- 
tinal tube  and  of  its  intestinal  glands  originates,  on  the 
other  hand,  from  the  intestinal-glandular  layer  (Fig.  290). 


TISSUES.  363 

Connective  tissue  (connectivum)  must  be  regarded  as 
forming,  in  order  of  phylogenetic  age,  the  second  main 
group  of  tissues.  This  is  morphologically  characterized  by 
the  intercellular   substance,  which    develops   between  the 


Fig.  291. — Jelly-like  tissue  from  the  vitreous  body  of  an  embryo  of  four 
months  (round  cells  as  jelly-like  intercellular  substance). 

Fig.  292. — Cartilage-tissue  of  the  fibrous  or  netted  cartilage  of  the  ear- 
shell  :  a,  cells  ;  6,  intercellular  mass  ;  c,  fibres  in  the  latter.     (After  Frey. ) 

cells,  physiologically,  by  the  double  part  which  it  plays, 
as  connecting  substance  and  as  complementary  substance 
between  the  other  tissues,  as  an  inner  supporting  substance 
and  as  a  protective  covering  for  the  inner  organs.  Of  the 
numerous  forms  and  varieties  of  connective  tissue,  we  regard 
the  jelly-like  tissue  (Fig.  291  ;  Fig.  G,  vol.  i.  p.  126),  the  fatty 
tissue,  and  the  chorda  tissue  as  the  earlier ;  the  fibrous, 
cartilaginous  (Fig.  292),  and  bone-tissue  (Fig.  5,  vol.  i.  p.  12G) 
as  the  more  recent  formations.  All  these  various  forms  of 
connective  tissue  are  products  of  the  middle  germ-layer, 
or  mesoderm  ;  or,  more  accurately,  of  the  two  fibrous  layers, 
of  which  the  skin-fibrous  layer  is  originally  derived  from 
the  exoderm,  the  intestinal-fibrous  layer  from  the  entoderm. 
The  nerve-muscular  tissue  (neuro-musculum)  is  of  much 
more  recent  origin  than  the  connective  tissue.  If  epithelial 
tissue  represents  a  primary  period  in  tribal  history,  and 


364 


THE   EVOLUTION   OF  MAN. 


connective  tissue  a  secondary  period,  then  we   may  cha- 
racterize a  third,  much  later  period,  by  nerve-muscle  tissue. 


Fig.  293. 


Fia.  295. 


Fig.  294. 


Fig.  293. — Nerve-muscle  tissue.  Three  cells  from  Hydra:  n,  outer, 
nervous  ;  m,  inner,  muscular  part  of  the  cells.     (After  Kleinenberg.) 

Fig.  294. — Nerve-tissue  (from  a  spinal  nerve  knot)  :  a,  anterior,  b, 
posterior  root  of  the  spinal  nerve  ;  d,  e,  fibrous  nerve-stem ;  /,  g,  h,  i,  nerve 
cells  in  ganglion  (f,  unipolar,  g,  h,  bipolar  cells) ;  I;  I,  nerve  fibres.  (After 
Frey.) 

Fig.  295. — Muscle-tissue.  Three  pieces  of  striped  muscle  fibre  (a).  Tn- 
terfibrous  fat-cells  (b).     (After  Frey.) 

For  while  in  the  lowest  Plant  Animals  the  body  consists 
merely    of    covering    tissue,   and    while    in    many    other 


TISSUES. 


365 


Zoophytes  a  middle  layer  of  connective  tissue  develops 
between  the  two  primary  germ-layers,  it  is  only  in  the 
most  highly  developed  Plant  Animals  that  muscle  and  nerve 
tissue  is  formed.  As  has  already  been  said,  the  latter  first 
appeared  as  a  common  nerve  and  muscle  tissue  (neuro- 
musculum,  Fig.  293  ;  cf.  p.  358).  It  was  only  afterwards 
that  the  muscle-tissue  (Fig.  295)  separated  from  the  nerve- 
tissue  (Fig.  294).  The  greater  part  of  the  nerve-tissue  is 
derived  from  the  skin-sensory  layer,  the  greater  part  of  the 
muscle-tissue  from  the  skin-fibrous  layer. 

Vascular  tissue  (vasalium)  must  be  regarded  as  forming 


Fig.  29G. —  Vascular  tissue  (vasalium).  A  hair- vessel  from  the 
mesentery  :  a,  vasculsir  cells  ;   b,  the  kernels  of  these  ("  endothelium"). 

FlO.  21)7- — Red  blood  cells  (corpuscles)  of  various  Vertebrates  (equally 
magnified):  1,  Human;  2,  Camel ;  3,  Pigeon;  4,  Proteus  (p.  129);  5,  Water- 
salamander  (Triton) ;  6,  Frog  ;  7,  Fish  (Cobitis) ;  8,  Lamprey  (Petromyzon)  ; 
a,  surface  view  ;  b,  edge  view.     (After  ^Yagncl•.) 


(     366    ) 

TABLE    XXXVIII. 

Systematic  Surrey  of  the  Sequence,  according  to  Age,  of  the  Human 

Tissue-groups. 

(Phylogenetic  Classification  of  Vertebrate  Tissues.) 


FIRST  GROUP:   PRIMARY  TISSUES   {Epithelium). 

1.  First  Histological  Stage  of  Evolution. 
I.  Covering-tissue  {Epithelium). 
I.  A.   Skin-covering   tissue    (EpMelium   dermale)  (\  gS^i^^ 

01-:„    1 „,.     V.-„,Wvr,      «f   P.iclrnli     /„„.„_/   ^.    <' LU  Ills  (Jl  Ollt(_  T  Skill 


Skin-layer,  or  Exoderm,  of  Gastrula  (after- 
wards skin-sensory  layer) 


3.  (Earliest  site  of  origin  of  the  sperm- 
cells  .') 

I.  B.  Intestinal  covering  tissue  (Epi/hel.  pastrale).  (1.  Real  intestinal  epithelium 

Intestinal    layer,  or    Entoderm,  of   Gastrula  <  2.  Epithelium  of  the  intestinal  glands 
(afterwards  the  intestinal-glandular  layer)       (  3.  ( Earliest  site  of  origin  of  egg-cell  ?) 

SECOND  GROUP:    SECONDARY  TISSUES. 
(All  derived  from  the  Covering-tissue,  or  Epithelium.) 

2.  Second  Histological  Stage  of  Evolution. 
II.  Connective -tissue  (Connectivum). 

II.  C.  Filling-up  tissue  (Tela  conjunctiva)  (softer  |  2"  p  iuV  t\ssueSSUe 

[surrounding]  connective  tissue)  j  3'  Fibrous  Tissue 

TT   _    „  ,.        ..  ,m,       ,  T  .     .  »   ra  1 4.  Chorda  tissue 

II.  D.  Supporting  tissue   (Tela  sJceletans)  (firmer!  g   cartilaginous  ttasne 

(  6.  Bone-tissue 


[supporting]  connective  tissue) 


III 


III.  E.  Nerve-tissue      (Tela 
nervea}.  Original  outer  I 

portion  of  the  nerve-  \ 
muscle    cells    of    the 
Exoderm  I 

F.  Muscle-tissue     (Tela  { 
muscularis)  Original 
inner  portion  of  the 
nerve-muscle  cells  of 
the  Exoderm 


3.  Third  Histological  Stag 
III.  Nerve-muscle  Tissue  (iV 


Nerve-cells 
(Ganglion-cells) 

Nerve-fibres 
(N'erve-tubes) 


1.  One-celled  muscle-  f  1 
fibres  ( l 

2.  Many-celled  muscle-  (  2 
fibres  \  2 


e  of  Evolution. 
euro-musculum). 
a.  Peripheric  nerve-cells  (I!od -cells  of 

the  sense-organs) 
o.  Central  nerve-cells  (mind-cells) 
a.  Sheath  less    nerve-fibres    (pale,    or 

medulla-less  fibres) 
6.  Sheathed  nerve-fibres  (dark  fibres 

with  medulla) 

a.  Smooth  contractile  fibre-cells 

b.  Stiiped  contractile  fibre-Cells 

a.  Smooth  muscle-masses 

b.  Striped  muscle-masses 


4.  Fourth  Histological  Stage  of  Evolution. 
IV.  Vascular  Tissue  (Vasalrum). 


IV.  67.  Vascularizing  tissue 
(Tela  vasalis).  Inner 
wall-covering  of  the 
Ccelom  system 


1.  Coelarium 

(Ccelom  -  epithe- 
lium) 


(' 


1.  a.  Exocoelarium  (Parietal  Ccelom-epi- 
thelium)  (and  secondary  site  of 
origin  of  the  sperm-cells  ?) 
6.  Endoccelarium  (Visceral  coelom-epi- 
thelium)  (and  secondary  site  of 
origin  of  the  egg-cells  ?) 


a.  Endothelium  of  the  lymph-vessels 

b.  Endothelium  of  the  blood-vessels 


Endothelium 
(Vascular  epithe 
\  lium) 

IV.  H.  Lymph-tissue    (Tela  f 

lt/mpkatica).     Liquid  J  I.  Lymph  (Colourless  blood-cells  and  fluid  intercellular  substance) 
contents  of  theCudom  1  2.  Bluod  (Red  blood-cells  and  fluid  intercellular  substance) 
system  I 


(     3^7    ) 
TABLE    XXXIX. 

Systematic  Survey  of  the  Sequence,  according  to  Age,  of  the  Human 
Organ-systems. 
(Phylogenetic  Classification  of  Vertebrate  Organs.) 
(On  the  right  are  given  the  Ancestral  Stages,  in  which  the  respective 
organs  probably  first  appeared.) 

1.  First  Stage  ^in  the  Evolution  ok  Organs. 

I.  Skin  and  Intestinal  Systems. 

The  two  Systems  appear  first,  and  simultaneously,  in  the  Gastread  ancestors. 

/  A  1.  Simple  exoderm  Gastraads 

I.  A.  Skin-system  i  A  2.  Outer    skin   (Skin-sensory  layer)  and  )  wormg 

(JSytttma  dermale)         \  leather  skin  (Skin-fibrous  layer)  J 

'  A  3.  Outer  skin,  with  hairs,  glands,  etc.  Mammals 

!B  1.  Simple  entoderm  Gastra.'ads 

B  2.  Intestinal  epithelium  (Intestinal-plan-  \ 
dular  layer)  and  intestinal  muscular  J  Worms 
skin  (Intestinal-fibrous  layer)  j 

BZ.  Gill-intestine  and  stomach-intestine        Chorda-animals 

2.  Second  Stage  in  the  Evolution  of  Organs. 

II.  Nerve  and  Muscle  Systems. 

The  two  Systems  appear  first,  and  simultaneously,  in  the  Primitive  AVorm  ancestors. 
Ti  r  N,rve  svstem  (  C 1.  Upper  throat  ganglia  Primitive  Worms 

taZSa^amU  C  2"  SimPle  medullary  tube  Chorda-animals 

{Systana  net  leum)        |  c  3   B|..Un  and  gpinal  marrow  Monorhina 

TT  n   Muscle-svstem  (  Z>  1.  Skin-muscle  pouch  Primitive  Worms 

II.  u.  MOSC'e  bj  Ntem  )  I)  2.  Side  muscles  of  the  trunk  Acrania 

(Systema  muscalare)     \  D  3   Trunk  and  ,imb  nmsdcg  Fis.hes 

3.  Third  Stage  in  the  Evolution  of  Organs. 

III.  Kidney  and  Vascular  Systems. 

The  two  Systems  fir.-.t  appear,  one  after  the  other,  in  the  Soft-worm  ancestors  (Scolecida'). 

(E\.  Primitive  kidney  canals  Scolecida 

III.  E.  Kidney-system  1A'2.  Segmental  canals  Acrania? 

(Sijs  ema  renale)  j  E3.  Primitive  kidneys  Monorhina 

\E4.  Permanent  kidneys  Protamnia 

(  F\.  Simple  ccelom  Scolecida 
)F2.  ~ 


III.  F.  Vascular  system  )  F2.  Dorsal  and  ventral  vessels  Worms 

"l  F3.  Heart  (part  of  the  ventral  vessel)  Chorda- 

.  Fi.  Heart,  with  auricle  and  ventricle  Monorhina 


(Systema  vasculare')     ~)  F3.  Heart  (part  of  the  ventral  vessel)  Chorda-animals 


4.  Fourth  Stage  in  the  Evolution  of  Organs. 

IV.  Skeleton  and  Sexual  Systems. 

The  two  Systems  first  appear,  one  after  the  other,  in  the  Chordonia-ancestors. 

rOl.  Simple  notochord  Chorda-animals 

IV.  G.  Skeleton-system             Iff  3.  Cartilaginous  primitive  skull  Monorhina 

(J3]/8tema  skdtlare)      "j  c:\.  Gill-arches,  ribs,  limbs  Sclichii 
\Gi.  Limbs,  with  live  digits 


Amphibia 
Chorda-i 
IV.  n.  Sexual  syBtem  J  y/2.  Distinct  testes  and  ovaries  Acrania 

-duct  and  oviduct  Selachii 

lus  (penis,  clitoris)  Protamnia 


fill.  Simple  hermaphrodite  glands  Chorda-animals 

)  III.  Iiistinct  testes  and  ovaries 


[Syttema  sexuale)         )  113.  Seed-duct  and  oviduct  Belach 

lz/4.  Phallus  ' 


39 


368  THE   EVOLUTION   OF   MAN. 

the  most  recent  group  of  tissues,  that  which  originated  last. 
Under  this  name  are  included  those  epithelial-like  tissues 
which  line  the  closed  inner  cavities  of  the  body  (the  ccelom, 
chest-cavity,  ventral  cavity,  heart-cavity,  blood-vessels,  etc. 
(Fig.  296).  In  addition  to  this  vascular  carpet  (endo- 
thelium), the  liquids  containing  cells,  which  fill  these 
cavities  (lymph,  blood,  serum,  etc.),  must  be  classed  with 
this  tissue  (Fig.  297)-  All  these  tissues  may  be  grouped  as 
vasalia.  His  wrongly  ascribed  to  them  a  quite  different, 
" parablastic "  origin  (from  the  nutritive  yelk);  they  are, 
however,  products  of  the  intestinal-fibrous  layer  (and  partly, 
perhaps,  of  the  skin-fibrous  layer).  As  the  coeloma  and  the 
whole  vascular  system  is  of  more  recent  phylogenetic  origin, 
its  peculiar  tissues  must  also  be  more  recent. 

This  phylogenetic  explanation  of  the  ontogenetic  suc- 
cession of  the  tissues  and  of  the  organ  systems  arising  from 
them,  appears  to  me  to  be  satisfactorily  proved  by  Com- 
parative Anatomy,  and  by  the  Gastrcea  theory.  If  it  is 
correct,  it  discloses  an  interesting  glimpse  into  the  entirely 
various  age  of  the  most  important  constituent  parts  of  our 
bod}^.  The  human  skin  and  intestine  are,  according  to  this, 
many  thousands  of  years  older  than  the  muscles  and  nerves; 
these  again  are  much  more  ancient  than  kidneys  and  blood- 
vessels, and  the  latter,  finally,  are  many  thousands  of  years 
older  than  the  skeleton  and  the  sexual  organs.  The  com- 
mon view,  that  the  vascular  system  is  one  of  the  most 
important  and  original  organ-systems,  is,  therefore,  erro- 
neous ;  it  is  as  false  as  the  assumption  of  Aristotle  that 
the  heart  is  the  first  part  to  form  in  the  incubated  chick. 
On  the  contrary,  all  lower  Intestinal  Animals  show  plainly 
that  the  historic  evolution  of  the  vascular  system  did  not 


RUDIMENTARY   VASCULAR   SYSTEM.  369 

begin  till  a  comparatively  late  period.  Not  only  all  Plant 
Animals  (Sponges,  Corals,  Hydropolyps,  Medusas),  but  also 
all  lower  Worms  (Acoelomi),  are  entirely  destitute  of 
vascular  system.  In  both  groups,  the  fluid  acquired  by 
digestion  is  conveyed  directly  from  the  intestinal  tube, 
through  processes  of  this  latter  (the  gastro-canals),  into  the 
different  parts  of  the  body.  It  is  only  in  the  intermediate 
and  higher  Worms  that  the  vascular  system  first  begins  to 
develop,  in  consequence  of  the  formation  of  a  simple  cavity 
(coeloma),  or  of  a  system  of  connected  spaces,  round  the 
intestinal  tube,  in  which  cavities  the  nutritive  fluid  (blood) 
exuded  through  the  intestinal  wall,  collects. 

In  the  human  ancestral  line  we  meet  with  this  first 
rudiment  of  the  vascular  system  in  that  group  of  Worms 
which  we  spoke  of  as  Soft  Worms  (Scolecida;  p.  85). 
The  Soft  Worms,  as  we  said,  formed  a  series  of  intermediate 
stages  between  the  lowest  bloodless  Primitive  Worms 
(Archelminthes)  and  the  Chorda- worms  (Chordoma),  which 
are  already  provided  with  a  vascular  system  and  a  noto- 
chord.  The  vascular  system  must  have  begun,  in  the  older 
Scolecida,  with  a  very  simple  ccelom,  a  "body-cavity," 
filled  with  blood,  and  which  surrounded  the  intestinal  tube. 
Its  origin  was  probably  due  to  the  accumulation  of 
nutritive  fluid  in  a  cleft  between  the  intestinal-fibrous 
layer  and  the  skin-fibrous  layer.  A  vascular  system  in 
this  simplest  form  is  yet  found  in  the  Moss-polyps  (Bryozoa) 
in  the  Wheel-animalcule  (Rotatoria),  and  in  other  lower 
Wonns.  The  inner,  visceral,  part  of  the  wall  of  the  ccelom 
is,  naturally,  formed  by  the  intestinal-fibrous  layer  (endo- 
coelar),  the  outer,  parietal,  part  by  the  skin-fibrous  layer 
(exocozlar).     The  ccelom  fluid,  collected  between  the  two, 


370  THE   EVOLUTION   OF   MAN. 

may  contain  detached  cells  (lymph-cells)  from  either  fibrous 
layer. 

A  first  advance  in  the  development  of  this  most  primi- 
tive vascular  system  was  accomplished  by  the  formation  of 
canals  or  blood-conducting  tubes,  which  developed,  inde- 
pendently of  the  coeloma,  in  the  intestinal  wall,  that  is,  in 
the  intestinal-fibrous  layer  of  the  wall.  These  real  blood- 
vessels, in  the  stricter  sense,  appear  in  very  different 
form  in  Worms  of  the  intermediate  and  higher  groups  ; 
sometimes  they  are  very  simple,  sometimes  very  complex. 
Two  primordial  "primitive  vessels"  must  be  regarded  as 
representing  that  form,  which  probably  formed  the  first  of 
the  more  complex  vascular  system  of  Vertebrates ;  these  are 
a  dorsal  vessel,  which  passes  from  front  to  back  along  the 
middle  line  of  the  dorsal  wall  of  the  intestine,  and  a  ventral 
vessel  which  passes,  in  the  same  direction,  along  the  middle 
line  of  the  ventral  wall.  Both  at  the  front  and  at  the 
back  these  two  vessels  are  linked  together  by  a  loop  sur- 
rounding the  intestines.  The  blood  enclosed  in  the  two 
tubes  is  driven  forward  by  the  peristaltic  contraction  of 
this. 

The  further  development  of  this  simplest  rudimentary 
blood-vessel  system  is  evident  in  the  class  of  the  Ringed 
"Worms  (Annelida),  in  which  we  find  it  in  very  various 
stages  of  development.  In  the  first  place,  many  trans- 
verse connections  probably  arose  between  the  dorsal  and 
ventral  vessels,  so  as  to  encircle  the  intestine  (Fig.  298). 
Other  vessels  then  penetrated  into  the  body-wall  and 
branched,  so  as  to  conduct  blood  to  this  part.  As  in  those 
ancestral  Worms,  which  we  have  called  Chordoma,  the 
front  section  of  the  intestine  changed  into  a  gill-body,  these 


THE   VASCULAR   SYSTEM. 


371 


ascular  loops,  within  the  wall  of  this  gill-body,  which 
passed  from  the  ventral  vessel  to  the  dorsal  vessel,  became 
modified  into  respiratory  gill-vessels.  Even  at  the  present 
day,  the  organization  of  the  remarkable  Acorn-worm 
(Balanoglossus)  exhibits  a  similar  condition  of  gill-circula- 
tion (Fig.  186,  p.  86). 

A  further  important  advance  is  exhibited, 
among  extant  Worms,  in  the  Ascidia,  which 
must  be  regarded  as  the  nearest  blood-rela- 
tions to  our  primitive  Chordoma  ancestors. 
In  these  we  find,  for  the  first  time,  a  real 
heart,  that  is,  a  central  organ  of  the  circula- 
tion of  the  blood,  by  the  pulsating  contractions 
of  the  muscular  wall  of  which  the  blood  is 
driven  forward  in  the  vascular  tubes.  The 
heart  appears  here  in  the  simplest  form,  as 
a  spindle-shaped  pouch  which  passes  at  both 
ends  into  a  main  vessel  (Fig.  188,  c.  p.  90; 
Plate  XI.  Fig.  14,  hz).     The  original  position 

Fig.  298. — Blood-vessel  system  of  a  Ringed  Worm 
(Saennris) ;  front  section:  d,  dorsal  vessel;  r,  ventral 
vessel ;  c,  transverse  connection  between  the  two  (en- 
larged  like  a  heart).  The  arrows  indicate  the  direction  of 
the  blood  current.     (After  Gegenbaur.) 

of  the  heart  on  the  ventral  side,  behind  the  gill-body  of  the 
Ascidian,  plainly  shows  that  it  originated  in  a  local  dilation 
of  a  section  of  the  ventral  vessel.  The  alternating  direc- 
tion of  the  movements  of  the  blood,  which  has  already  been 
mentioned,  is  remarkable  ;  the  heart  expels  the  blood  alter- 
nately through  the  anterior  and  through  the  posterior  end. 
This  is  very  suggestive,  because  in  most  Worms  the  blood 


$J2  THE   EVOLUTION    OF   MAN. 

in  the  dorsal  vessel  moves  from  back  to  front,  while  in 
Vertebrates,  on  the  contrary,  it  flows  in  the  opposite  direc- 
tion, from  front  to  back.  As  the  heart  of  the  Ascidian 
constantly  alternates  between  these  two  opposite  directions, 
it  exhibits  permanently,  to  a  certain  extent,  the  phylogenetic 
transition  between  the  older  direction  of  the  dorsal  blood- 
current  toward  the  front  in  Worms,  and  the  newer  direc- 
tion of  the  same  toward  the  rear  in  Vertebrates. 

As  in  the  more  recent  Chorda  Animals,  which  gave 
rise  to  the  Vertebrate  tribe,  the  newer  direction  became 
permanent,  the  two  vessels  which  proceeded  from  the 
two  ends  of  the  heart-pouch,  acquired  a  constant  signifi- 
cance. The  front  section  of  the  ventral  vessel,  since  then, 
has  steadily  conducted  the  blood  from  the  heart,  acting, 
consequently,  as  an  artery ;  the  hinder  section  of  the 
ventral  vessel,  on  the  contrary,  leads  the  blood,  circulating 
in  the  body,  back  into  the  heart,  and  must,  therefore,  be 
called  a  vein.  In  reference  to  their  relation  to  the  two 
sections  of  the  intestine,  we  may  speak  of  the  latter,  more 
accurately,  as  the  intestinal  vein,  and  of  the  former  as  the 
gill-artery.  The  blood  contained  in  both  vessels,  which 
alone  fills  the  heart  also,  is  venous  blood  ;  that  is,  containing 
much  carbonic  acid.  On  the  other  hand,  the  blood  which 
flows  from  the  gills  into  the  dorsal  vessel  is  there  re- 
furnished with  oxygen ;  is  arterial  blood.  The  most  delicate 
branches  of  the  arteries  and  veins  pass  into  each  other, 
within  the  tissue,  through  a  network  of  extremely  fine 
neutral  hair-vessels  or  capillaries  (Fig.  296). 

If  we  now  turn  from  the  Ascidia  to  the  nearest  allied 
form,  the  Amphioxus,  we  are  immediately  surprised  by  an 
apparent  retrogression  in  the  development  of  the  vascular 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM.      ^73 

system.  The  Amphioxus,  as  has  been  stated,  has  no  real 
heart ;  but  the  blood  is  circulated  in  its  vascular  system  by 
the  main  vascular  stems  themselves,  which  contract  and 
pulsate  along  their  whole  length.  (Cf.  Fig.  151,  vol.  i.  p.  420.) 
A  dorsal  vessel  (aorta),  situated  over  the  intestine,  absorbs 
the  arterial  blood  from  the  gills  and  propels  it  through  the 
body.  The  venous  blood,  in  its  return,  collects  in  a  ventral 
vessel  (intestinal  vein),  situated  under  the  intestine,  and 
thus  returns  to  the  gills.  Numerous  vascular  gill-arches, 
which  accomplish  respiration,  and  absorb  oxygen  from  the 
water  and  emit  carbonic  acid,  unite  the  ventral  vessel 
with  the  dorsal  vessel  before.  As,  in  Ascidia,  that  section 
of  the  ventral  vessel  which  also  forms  the  heart  in  Skulled 
Animals  (Craniota),  is  already  fully  developed  into  a  simple 
heart-pouch,  we  must  regard  the  absence  of  the  latter  in  the 
Amphioxus  as  the  result  of  retrogression,  as  a  reversion,  in 
these  Acrania,  to  the  older  form  of  vascular  system,  as  it 
exists  in  Scolecida  and  many  other  Worms.  We  may 
assume  that  those  Acrania  which  actually  formed  part  of 
our  ancestral  line  did  not  share  this  relapse,  but  rather 
inherited  the  one-chambered  heart  from  the  Chordoma  and 
transmitted  it  directly  to  the  older  Skulled  Animals 
(Craniota). 

The  Comparative  Anatomy  of  Skulled  Animals  clearly 
exhibits  the  further  phylogenetic  development  of  the  blood- 
vessel system.  In  the  lowest  stage  of  this  group,  in  the 
Cyclostonia  (p.  102),  we  first  meet  with  a  real  lymph-vessel 
system,  side  by  side  with  the  blood-vessel  system,  a  system 
of  canals  which  collect  the  colourless  fluid  flowing  from  the 
tissues,  and  conduct  it  to  the  blood-current.  Those  lymph- 
vessels    which   absorb  the  milky,  nutritive  fluid,  obtained 


374  THE  EVOLUTION   OF   MAN. 

directly  by  digestion,  from  the  intestinal  wall,  and  conduct 
it  to  the  blood-current,  are  distinguishable  as  chyle-vessels, 
or  "milky  juice  vessels."  While  the  chyle,  or  milky  juice, 
in  consequence  of  the  great  amount  of  fat  globules  which 
it  contains,  appears  milk  white,  the  real  lymph  is  colour- 
less. The  chyle,  as  well  as  the  lymph,  contain  the  same 
colourless  amoeboid  cells  (Fig.  9,  vol.  i.  p.  132),  which  are  also 
distributed  in  the  blood  as  colourless  blood-cells  (corpuscles) ; 
the  latter  contains,  in  addition,  the  much  greater  quantity 
of  red  blood-cells  (corpuscles),  which  gives  the  blood  of 
Skulled  Animals  its  red  colour.  The  distinction,  common  to 
all  Craniota,  between  lymph-vessels,  chyle-vessels,  and 
blood-vessels,  is  to  be  regarded  as  the  result  of  a  division  of 
labour  which  took  place  between  different  portions  of  an 
original  unitary,  primitive  blood-vessel  system  (or  hsemo- 
lymph  system). 

The  heart,  the  central  organ  of  the  circulation  of  the 
blood,  which  exists  in  all  Craniota,  also  exhibits  an  advance 
in  structure,  even  in  the  Cyclostoma.  The  simple  spindle- 
shaped  heart-pouch  is  separated  into  two  divisions,  or 
chambers,  which  are  divided  by  two  valves  (Plate  XL 
Fig.  16,  hv,  hh).  The  posterior  division,  the  fore  chamber 
(atrium,  hv),  absorbs  the  venous  blood  from  the  veins  of 
the  body,  and  discharges  it  into  the  anterior  division,  the 
chamber,  or  main  chamber  (yentriculus,  hk).  From  here  it 
is  propelled  by  the  gill-artery  stem  (the  foremost  section  of 
the  ventral  vessel)  into  the  gills. 

In  Primitive  Fishes  (Selachii),  an  arterial  stalk  (bulbus 
arteriosus),  separated  by  valves,  originates,  as  a  distinct 
section,  from  the  foremost  end  of  the  ventricle.  It  forms 
the  enlarged,  hindmost  end  of  the  gill-artery  stem    (Fig. 


DEVELOPMENT  OF  THE  VASCULAR  SYSTEM. 


375 


299,  abr).  From  each  side  of  this,  from  five  to  seven  gill- 
arteries  proceed ;  these  rise  between  the  gill-openings  (,s) 
to  the  gill-arches,  encircle  the  throat,  and  combine  above 
into  a  common  aorta-stem,  the  continuation  of  which, 
passing  backward  above  the  intestine,  corresponds  to  the 
dorsal  vessel  of  Worms.  As  the  arched  arteries  distribute 
themselves  in  a  respiratory  capillary  net  over  the  gill- 
arches,  they  thus  contain  venous  blood  in  their  lower  part 
(as  arterial  gill-arches),  and  arterial  blood  in  their  upper 
part  (as  aorta-arches).  The  points  at  which  separate  aorta- 
arches  unite,  which  occur  on  the  right  and  left  sides,  are 
called  aorta-roots.  Of  an  originally  greater  number  of 
aorta-arches,  only  five  pairs  are  retained,  and  from  these 
five  (Fig.  300),  in  all  higher  Vertebrates,  the  most  im- 
portant parts  of  the  arterial  system  develop. 


Fig.  299. — Head  of  an  embryonic  Fish,  with  the  rudiment  and  the 
blood-vessel  system ;  seen  from  the  left  side  :  dc,  Cuverian  duct  (point  of 
union  of  the  front  and  hind  main  veins)  ;  sv,  venous  sinus  (enlarged 
terminal  portion  of  the  Cuverian  duct) ;  a,  auricle  ;  v,  main  chamber  ; 
abr,  gill-artery  stem ;  s,  gill-openings  (between  the  arterial  arches) ;  ad, 
aorta;  c',  head-artery  (carotis) ;  n,  nose-groove.     (After  Cegcnbaur.) 

The  appearance  of  the  lungs,  connected  with  the  respi- 
ration of  air,  which  first  occurs  in  the  Dipneusta,  is  most 
important   in    the    further    dcvelopement   of  the    arterial 


$76  THE   EVOLUTION   OF   MAN. 

system.  In  Dipneusta,  the  auricle  of  the  heart  separates 
into  two  halves  by  the  formation  of  an  incomplete  partition. 
Only  the  right  auricle  now  absorbs  the  venous  blood  of  the 
body-veins.  The  left  auricle,  on  the  other  hand,  absorbs 
the  arterial  blood  of  the  lung-veins ;  both  auricles  dis- 
charge in  common  into  the  simple  ventricle,  in  which  the 
two  kinds  of  blood  mingle,  and  are  then  propelled  through 
the  arterial  stalk  into  the  arterial  arches.  From  the  last  of 
these  latter  spring  the  lung-arteries  (Fig.  801,  p) ;  these 
convey  a  part  of  the  mixed  blood  into  the  lungs,  while  the 
remainder  is  driven  through  the  aorta  into  the  body. 

From  the   Dipneusta   upward,  we    trace    a   progressive 
development  of  the  vascular  system,  which  finally  leads, 
with  the  loss  of  gill  respiration,  to  a  complete  separation  of 
the  two  parts  of  the  double  circulatory  system.     In  Am- 
phibia, the   partition    between   the    two   auricles   becomes 
complete.       In   their   young   form,   these   yet    retain   gill- 
respiration  and  the  circulatory  system  as  in  Fishes,  and  the- 
heart  contains  only  venous  blood;    at  a  later  period,  the 
lungs,  with  their  vessels,  are  developed  also,  and  the  main 
chamber  of  the  heart  then  contains  mixed  blood.     In  Pro- 
tamnia  and  Reptiles,  the  main   chamber  and  the   arterial 
stalk  belonging  to  it  begin  to  separate,  by  the  formation  of 
a  longitudinal  partition,  into  two  halves,  and  this  partition 
becomes  complete  in  the  higher  reptiles  on  the  one  side,  in 
the  parent-form  of  Mammals  on  the  other.     The  right  half 
of  the  heart  alone  now  contains  venous  blood,  the  left  half 
only  arterial,  as    in   all    Birds   and   Mammals.     The  right 
auricle  receives  venous  blood  from  the  body-veins,  and  the 
right  ventricle  propels  this  through  the  lung-arteries  into 
the  lungs ;  from  there  it  returns  as  arterial  blood  through 


DOUBLE  CIRCULATORY  SYSTEM. 


377 


the  lung-veins  to  the  left  auricle,  and  is  driven  through  the 
left  ventricle  into  the  body-arteries.  Between  the  lung- 
arteries  and  lung-veins  is  situated  the  capillary  system  of 
the  lesser,  or  lung-circulation ;  between  the  body-arteries 
and  the  body-veins  lies  the  capillary  system  of  the  greater, 
or  body-circulation.     Only  in  the  two  highest  Vertebrate 


Fig.  300. — The  five  arterial  arches  of  Skulled  Animals  (1-5)  in  their 
original  form  :  a,  arterial  stalk ;  a",  main  stem  of  the  aorta  ;  c,  head- 
artery  (carotis,  anterior  continuation  of  the  aorta-roots).      (After  Rathke.) 

Fig.  301. — The  five  arterial  arches  of  Birds;  the  light  portions  of  the 
rudiment  disappear ;  only  the  dark  parts  are  permanent.  Letters  as  in 
Fig.  300  :  s,  arteries  of  the  clavicula  (sub-clavian)  ;  p,  lung-artery ;  p', 
branches  of  the  same.      (After  Rathke.) 

Fig.  302. — The  five  arterial  arches  of  Mammals.  Letters  as  in  Fig.  301 : 
v,  vertebral  artery ;  b,  Botalli's  duct  (open  in  the  embryo,  afterwards 
closed).     (After  Rathke.) 

classes,  in  Birds  and  Mammals,  is  this  complete  separation 
of  the  two  courses  of  the  circulation  perfect.  Moreover,  this 
separation  has  taken  place  in  the  two  classes  independently 
of  each  other,  as  is  shown  by  the  unequal  development  of 
the  aortas.     In  Birds,  which  are  descended  from  Reptiles, 


37$ 


THE   EVOLUTION   OF   MAN. 


the  right  half  of  the  fourth  arteiial  arch  has  become  the 
permanent  arterial  arch  (arcus  aortce,  Fig.  301).  On  the 
other  hand,  the  latter  has  developed  from  the  left  half  of 
the  same  arch  (Fig.  302)  in  Mammals,  which  are  directly 
descended  from  the  Protamnia. 

On  comparing  the  arterial  system  in  the  various  classes 
of  the  Skulled  Animals  (Craniota)  in  its  matured  condition, 
it  appears  in  very  various  forms,  and  yet  it  develops,  in 
all,  from  the  same  primitive  form.  This  development  takes 
place  in  man  exactly  as  in  other  Mammals ;  especially  is  the 
modification  of  the  five  arterial  arches  precisely  the  same  in 
both  cases  (Figs.  303-306).     At  first,  only  a  single  pair  of 


Figs.  303-306. — Metamorphosis  of  the  five  arterial  arches  in  the  human 
embryo  (diagram  after  Eathke) :  ta,  arterial  stalk ;  1,  2,  3,  4,  5,  the  arterial 
arches  from  the  first  to  the  fifth  pair ;  ad,  main  stem  of  the  aorta ;  aw, 
roots  of  the  aorta.  In  Fig.  303,  three  of  the  arterial  arches  are  given ;  in  Fig. 
304,  the  whole  five  (those  indicated  by  dots  are  not  yet  developed);  in  Fig.  305, 
the  first  two  have  again  disappeared  ;  in  Fig.  306,  the  permanent  arterial 
stems  are  represented.  The  dotted  parts  disappear,  s,  Snb-clavian  artery ; 
v,  vertebral  artery ;  ax,  axillary  artery ;  c,  carotid  artery  (c',  outer,  c", 
inner  carotis)  ;  p,  pulmonary  artery  (lung-artery). 

arches  develop,  and  these  lie  on  the  inner  surface  of  the 
first  pair  of  gill-arches  (Figs.  147-150,  vol.  i.  pp.  395-398; 
Fig.  303).     A  second  and  a  third  pair  of  arches  then  develop 


DEVELOPMENT  OF  THE  HEART.  379 

behind  the  first,  and  these  are  situated  on  the  inner  surface 
of  the  second  and  third  gill-arches.  At  length,  a  fourth  and 
a  fifth  pair  appear  behind  the  third  (Fig.  304) ;  but  while 
the  latter  are  developing,  the  first  two  are  again  disappear- 
ing by  growing  together  (Fig.  305).  The  permanent  main 
arteries  develop  only  from  the  three  posterior  arterial 
arches  (3,  4,  5,  in  Fig.  304),  the  lung-arteries  from  the  last 
(p ;  Fig.  306).     (Cf.  with  this  Fig.  302.) 

The  human  heart  also  (Fig.  314)  develops  exactly  like  that 
of  other  Mammals.  We  have  already  considered  the  first  prin- 
ciples of  its  germ-history  (vol.  i.  pp.  392-395,  Figs.  143-147), 
which  essentially  corresponds  with  its  Phylogeny.191  We  saw 
that  the  very  first  rudiment  of  the  heart  is  a  spindle-shaped 
thickening  of  the  intestinal-fibrous  layer  in  the  ventral  wall 
of  the  head-intestine  (Fig.  143,  df).  This  spindle-shaped 
formation  then  becomes  hollow,  forms  a  simple  pouch,  and 
separates  from  the  place  at  which  it  originated,  so  that  it 
then  lies  freely  in  the  cardiac  cavity  (Figs.  145,  14G).  This 
pouch  bends  into  the  form  of  an  S  (Fig.  144,  c),  and,  at  the 
same  time,  turns  spirally  on  an  imaginary  axis,  so  that  the 
posterior  part  lies  on  the  dorsal  surface  of  the  anterior 
part.  The  combined  yelk-veins  open  into  its  posterior 
extremity ;  from  the  anterior  extremity  proceed  the  arterial 
arches  (Fig.  150,  vol.  i.  p.  398). 

This  first  rudiment  of  the  human  heart,  which  encloses 
a  very  simple  cavity,  corresponds  to  the  heart  of  the  As- 
cidlans,  and  must  be  regarded  as  a  reproduction  of  the  heart 
of  the  Chordoma ;  it  now,  however,  separates  into  two,  and 
then  three  parts,  thus  exhibiting  for  a  very  brief  period  the 
heart-structure  of  the  Cyclostoma  and  of  Fishes.  The  spiral 
turn  and  curve  of  the  heart  increases,  and,  simultaneously, 


38o 


THE   EVOLUTION    OF   MAN. 


two  shallow  transverse  indentations  of  the  circumference 
appear,  which  externally  mark  the  three  sections  (Figs.  307, 
308).      The  anterior  section,  which  is  turned  toward   the 


Fig.  307. — Heart  of  an  embryonic  Rabbit,  from  behind  :  a,  yelk-veins  ; 
b,  auriculas  ;  c,  auricle  (atrium)  ;  d,  ventricle;  e,  artery-stalk;  /,  base  of  the 
three  pairs  of  arterial  arches.     (After  Bischoff.) 

Fig.  308. — Heart  of  the  same  embryo  (Fig.  307),  from  the  front :  v, 
yelk-veins ;  a,  auricle ;  ca,  auricular  canal ;  7,  left  ventricle ;  r,  right 
ventricle  ;  ta,  artery-stalk.      (After  Bischoff.) 

Fig.  309. — Heart  and  head  of  an  embryonic  Dog,  from  the  front: 
a,  fore-brain  ;  b,  eyes ;  c,  mid-brain ;  d,  primitive  lower  jaw  ;  e,  primitive 
upper  jaw  ;  /,  gill-arches  ;  g,  right  auricle  ;  h,  left  auricle  ;  i,  left  ventricle  ; 
fe,  right  ventricle.     (After  Bischoff.) 

Fig.  310. — Heart  of  the  same  embryo,  from  behind  :  a,  entrance  of  the 
yelk-veins  ;  b,  left  auricular  pi'ocess  ;  c,  right  auricular  process  ;  d,  auricle  ; 
e,  auricular  canal ;  /,  left  ventricle ;  g,  right  ventricle ;  h,  artery-stalk. 
(After  Bischoff.) 

ventral  side,  and  from  which  the  aortal  arches  spring, 
reproduces  the  arterial  stalk  (bulbils  arteriosus)  of  the 
Selachii.  The  central  section  is  the  rudiment  of  a  simple 
chamber,  or  ventricle  (ventriculus)  ;  and  the  posterior 
section,  the  one  turned  toward  the  dorsal  side,  into  which 
the  yelk-veins  open,  is  the  rudiment  of  a  simple  auricle 


DEVELOPMENT  OF   THE   HEART.  38 1 

(atrium).  The  latter,  like  the  simple  auricle  of  the  heart 
of  the  Fish,  forms  a  pair  of  lateral  protuberances,  the  heart 
ears,  or  auricular  appendages  {auricula},  Fig.  307,  b) ;  and 
hence  the  indentation  between  the  auricle  and  ventricle  is 
called  the  auricular  canal  {canalis  auricularis,  Fig.  308,  ca). 
The  heart  of  the  human  embryo  is  now  a  complete  Fish 
heart. 

Corresponding  exactly  with  the  Phylogeny  of  the  human 
heart  (Table  XLI ),  its  Ontogeny  exhibits  a  gradual  tran- 
sition from  the  Fish  heart  through  the  Amphibian  heart  to 
the  Mammalian  heart.     The  most  important  step  in  this 
advance  is  the  formation  of  a  longitudinal  partition,  im- 
perfect at  first,  afterwards  complete,  by  which  all  the  three 
sections  of  the  heart  are  separated  into  a  right  (venous)  and 
a  left  (arterial)   half.      (Cf.  Figs.  309-314.)      The   auricle 
(atrium)  is  thus  divided  into  a  right  and  a  left  auricle,  each 
of  which  acquires  its  respective  auricular  process ;  the  body- 
veins  discharge  into  the  right  auricle  (ascending  and  de- 
scending vena  cavce,  Fig.  311,  c,  Fig.  313,  c) ;  the  left  auricle 
receives   the   lung-veins.      Similarly,    a   superficial   "inter- 
ventricular furrow"  {sulcus  interventricular  is,  Fig.  312,  s) 
appears  at  an  early  period  on  the  main  chamber  of  the 
heart,  the  external  expression  of  the  internal  partition,  by 
the  formation  of  which  the  ventricle  is  divided  into  two 
chambers,  a  right  (venous)   and  a  left   (arterial)  ventricle. 
Finally,   a  longitudinal   partition  forms,  in  a  similar  way, 
in  the  third  section  of  the  primitive  heart,  which  so  much 
resembles  that  of  a  Fish,  in  the  arterial  stalk,  which  is  also 
externally  indicated  by  a  longitudinal  furrow  (Fig.  312,  of). 
This   separates    the    cavity    of  the    artery-stalk   into    two 
lateral  halves ;  the  main  lung  artery,  which  opens  into  the 


382 


THE   EVOLUTION   OF  MAN. 


Fig.  311. 


Fig.  313. 


Fig.  311. 


Fig.  311. —  Heart  of  a  human  embryo  of  four  weeks  ;  1,  from  the  front; 
2,  from  the  back  ;  3,  open,  and  with  the  upper  half  of  the  auricle  removed  ; 
a',  left  auricular  process  ;  a",  right  auricular  process ;  v',  left  ventricle  ; 
v",  right  ventricle  ;  ao,  artery-stalk ;  c,  upper  hollow  vein  (vena  cava)  (cd, 
right,  cs,  left)  ;  s,  rudiment  of  the  partition,  between  the  chambers.  (After 
Koelliker.) 

Fig.  312. — Heart  of  a  human  embryo  of  six  weeks,  from  the  front: 
r,  right  ventricle  ;  t,  left  ventricle  ;  s,  furrow  between  the  two  ventricles  ; 
ta,  artery-stalk ;  af,  furrow  on  its  surface ;  at  the  right  and  left  are  the 
two  large  auricular  processes  of  the  heart.     (After  Ecker.) 

Fig.  313. — Heart  of  a  human  embryo  of  eight  weeks,  from  behind : 
a',  left  auricular  process  ;  a",  right  auricular  process  ;  v',  left  ventricle ; 
v",  right  ventricle ;  cd,',  right  upper  vena  cava  ;  cs,  left  upper  vena  cava ; 
ci,  lower  vena  cava.     (After  Koelliker.) 

Fig.  314. — Heart  of  human  adult,  perfectly  developed,  from  the  front,  in 
its  natural  position  :  a,  right  auricular  process  (below  it,  the  right  ventricle)  ; 
b,  left  auricular  process  (below  it,  the  left  ventricle) ;  C,  upper  vena  cava; 
V,  lung-veins  ;  P,  lung-artery  ;  d,  Botalli's  duct ;  A,  aorta.     (After  Meyer.) 


right  ventricle,  and  the  aorta-trunk,  which  opens  into  the 
left  ventricle.  Not  until  all  these  partitions  are  complete, 
is  the  lesser,  or  lung-circulation,  entirely  distinct  from  the 


POSITION   OF   THE   RUDIMENTARY   HEART.  383 

greater,  or  bod}^-circulation  ;  the  right  half  of  the  heart  is 
the  centre  of  motion  for  the  former,  the  left  half  for  the 
latter.     (Cf.  Table  XLI.) 

In  the  human  embryo,  and  in  all  other  Amniota,  the 
heart  originally  lies  far  forward  on  the  lower  side  of  the 
head,  as  in  Fishes  it  remains  permanently  near  the  throat. 
Afterwards,  with  the  advancing  development  of  the  neck 
and  chest,  the  heart  continually  moves  further  back,  until 
at  last  it  is  situated  in  the  lower  part  of  the  breast  between 
the  lungs.  At  first  its  position  is  symmetrical,  in  the  central 
plane  of  the  body,  so  that  its  longitudinal  axis  corre- 
sponds with  that  of  the  body  (Plate  IV.  Fig.  8).  In  most 
Mammals  it  retains  this  symmetrical  position  permanently ; 
but  in  the  Apes  the  axis  begins  to  incline  obliquely,  and  to 
move  the  apex  of  the  heart  to  the  left  side.  This  inclination 
is  carried  furthest  in  the  Man-like  Apes;  in  the  Chim- 
panzee, Gorilla,  and  Orang,  which  also  resemble  Man  in 
this  oblique  position  of  the  heart. 

The  germ-history  of  all  other  parts  of  the  vascular  system, 
like  that  of  the  heart,  point  out  many  and  valuable  facts  re- 
garding the  history  of  our  descent.  But  as  an  accurate  know- 
ledge of  the  complex  arrangement  of  the  entire  vascular  system 
of  Man  and  other  Vertebrates  is  required,  in  order  to  follow  the 
matter  sufficiently  far  to  make  it  intelligible,  we  cannot  here 
enter  into  any  further  detail.192  Moreover,  many  important 
features  in  the  Ontogeny  of  the  vascular  system,  especially 
in  regard  to  the  derivation  of  its  various  parts  from  the 
secondary  germ-layers,  are  as  yet  very  obscure  and  doubtful. 
This  is  true,  for  example,  of  the  question  as  to  the  origin  of 
the  coelom-epithelium — that  is,  of  the  cell-layer  coating  the 
body-cavity.     Probably  there  is  an  important  phylogcnetic 


384  THE   EVOLUTION    OF   MAN. 

distinction  between  the  exoccelar,  or  the  parietal  ccelom- 
epithelium,  which  originates  from  the  skin-fibrous  layer,  and 
the  endoccelar,  or  the  visceral  ccelom-epitheliuni,  which 
is  derived  from  the  intestinal-fibrous  layer.  The  former 
is,  perhaps,  connected  with  the  male  germ-epithelium  (the 
rudiment  of  the  testes),  the  latter  with  the  female  germ- 
epithelium  (the  rudiment  of  the  ovary).    (Cf.  Chapter  XXV.) 


TABLE   XL. 

Systematic  Survey  of  the   most   important  Periods  in  the  Phylogeny 
of  the  Human  Vascular  System. 

I.  First  Period  :  Vascular  System  of  the  earlier  Scoleciala. 
Between  the  skin-covering  and  the  intestinal  wall  is  formed  a  simple 
body-cavity  {coeloma),  or  a  perienteric  cavity  (as  in  the  extant  Bryozoa  and 
other  Ccelomati). 

II.  Second  Period  :   Vascular  System  of  the  more  recent  Scolecida. 

The  first  real  blood-vessels  form  in  the  intestinal  wall  (in  the  intestinal- 
fibrous  layer),  a  dorsal  vessel  in  the  central  line  of  the  dorsal  side  of  the 
intestinal  tube,  and  a  ventral  vessel  in  the  central  line  of  its  ventral  side. 
The  two  vessels  are  connected  by  several  circular  vessels,  encircling  the 
intestine. 

III.   Third  Period  :   Vascular  System  of  the  earlier  Chordonia. 

By  the  modification  of  the  anterior  half  of  the  intestine  into  a  gill- 
intestine,  the  anterior  section  of  the  ventral  vessel  becomes  a  gill-artery, 
and  the  anterior  section  of  the  dorsal  vessel  a  gill-vein  ;  between  the  two 
a  gill  capillary  network  develojjs. 

IV.  Fourth  Period  :   Vascular  System  of  the  more  recent  Chordoma. 

The  portion  of  the  ventral  vessel,  lying  immediately  behind  the  gill- 
intestine,  enlarges  to  a  simple  heart-pouch  (Ascidiau). 


THYLOGENY   OF   THE   HUMAN   HEART.  385 

V.  Fifth  Period:   Vascular  System  of  the  Acrania. 

The  ventral  vessel  (intestinal  vein)  forms,  round  the  developing  liver- 
sac,  the  first  rudiment  of  a  vena  portae  system. 

VI.  Sixth  Period  :   Vascular  System  of  the  Cyclostomi. 

The  single-chambered  heart  divides  into  two  chambers ;  a  posterior 
ventricle,  and  an  anterior  auricle.  The  lymph-vessel  system  develops  side 
by  side  with  the  blood-vessel  system. 

V1JL  Seventh  Period  :   Vascular  System  of  the  Primitive  Fishes,  or  Selachii. 

From  the  anterior  section  of  the  main  chamber  of  the  heart  arises  an 
artery-stalk  or  trunk,  from  which  five  (?)  pairs  of  arterial  arches  proceed. 

VIII.  Eighth  Period:   Vascular  System  of  the  Mud-fishes. 
From  the  last  (fifth)  pair  of  arterial  arches  the  lung-arteries  develop, 
as  in  the  Dipneusta. 

IX.  Ninth  Period  :   Vascular  System  of  Amphilia. 

The  gill-arches  gradually  disappear  with  the  gills.  The  right  and  left 
aortal  arches  remain. 

X.  Tenth  Period  :  Vascular  System  of  Mammals. 

The  separation  of  the  greater  from  the  lesser  circulation  is  complete. 
The  right  aortal  arch  unites  with  Botalli's  duct. 


TABLE   XLI. 


Systematic  Survey  of  tiie   most  important  Periods  in  td.e  Phylogeny 
of  tue  Human  Heart. 

I.  First  Period  :  Heart  of  Chordoma. 

The  heart  forms  a  simple  spindle-shaped  enlargement  of  the  ventral 
vessel,  with  an  alternating  blood-current  (as  in  Ascidia). 

II.  Second  Period  :   Heart  of  Acrania. 

The  heart  is  like  that  of  Chordoma,  bat  the  blood-current  acquires 
a  constant  direction,  passing  only  from  back  to  front.  (Retrograded  in 
Amphioxus.) 


$86  THE   EVOLUTION   OF  MAN. 

III.  Third  Period  :  Heart  of  Cyclostoma. 

The  heart  divides  into  two  chambers,  a  posterior  auricle  (atrium)  and 
an  anterior  ventricle  (yentriculus). 

IV.  Fourth  Period  :  Heart  of  Primitive  Fishes. 
From  the  anterior  section  of  the  ventricle  is  differentiated  an  arterial 
stalk  (bulbus  arteriosus),  as  in  all  Selachii. 

V.  Fifth  Period  :  Heart  of  the  Mud-fishes. 

The  auricle  divides,  by  an  imperfect  and  interrupted  partition,  into 
a  right  and  a  left  half,  as  in  Dipneusta. 

VI.  Sixth  Period  :  Heart  of  Amvhibia. 

The  partition  between  the  right  and  left  auricles  becomes  complete,  as  in 
the  higher  Amphibia. 

VII.  Seventh  Period  :  Heart  of  Protamnia. 

The  main  chamber  of  the  heart  divides,  by  an  incomplete  partition,  into 
a  right  and  a  left  half,  as  in  Reptiles. 

VIII.  Eighth  Period  :  Heart  of  Monotrema. 

The  partition  between  the  right  and  left  ventricles  becomes  complete,  as 
in  all  Mammals. 

IX.  Ninth  Period  :  Heart  of  Marsupials. 

The  valves  between  the  auricles  and  ventricles  (atrio-ventricular  valves), 
together  with  the  connecting  filaments  and  papillary  muscles  belonging  to 
them,  are  differentiated  from  the  muscular  masses  of  Monotremes. 

X.  Tenth  Period  :   Heart  of  J  pes. 
The   main    axis   of    the  heart,   lying  in  the   central  line   of    the   body 
becomes  oblique,  so  that  the  apex  is  turned  to  the  left,  a3  in  Apes  and 
Mao. 


(     3S7     ) 


TABLE    XLII. 

Systematic  Survey  of  those  Primitive  Organs  which  must  probably  be 
regarded  as  homologous  in  "Worms,  Articulated  Animals,  Soft-bodied 
Animals,  and  Vertebrates.193 


Worms 
( Vermes). 


Articulated 

Animals 
(Arthropoda). 


Soft-bodied 
Animals 

(Mollusca). 


Vertebrates 
( Vertebrata). 


I.  Products  of  the  Differential 

ion  of  the  Skin-sensory  Layer. 

1.  Outer  skin 

(Epidermis) 

2.  Brain  (upper  throat- 

ganglia) 
2.  Excretory      organs 
(water  -  vessels, 
segmental  organs 

1.  Chitinous  skin 

(Ifi/podermis) 

2.  Brain  (upper  throat- 

ganglia) 

3.  Shell-glands  of  the 

Crustacean 
(trachea    of    the 
Tracheata  ?) 

1.  Outer  skin 

(Epidermis) 

2.  Brain  (upper  throat- 

ganglia) 

3.  Rudimentary    kid- 

neys    (Primitive 
kidneys) 

1.  Outer  skin 

(Epidermis) 

2.  Medullary  tube  (an- 

terior part) 

3.  Primitive      kidney- 

ducts     (Prolure- 
teres)    and     seg- 
mental organs 

II.  Products  of  the  Differentiation  of  the  Skin-fibrous  Layer. 


4.  Leather-skin 

4.  Leather-skin 

4.  Leather-skin 

4.  Leather-skin 

(Corium) 

(Uudiment) 

(Corium) 

(Corium} 

(together  with  the 

(together  with  the 

(together  with  the 

circular    muscle- 

muscles    of    the 

muscular  layer  of 

pouch  .') 

skin  ?) 

the  skin  ?) 

5.  Longitudinal 

5.  Trunk-muscles 

5.  Inner  trunk-muscles 

5.  Side  trunk-muscles 

muscle-pouch 

C.  Exoccelar  innermost 

6.  Exoccelar  innermost 

6.  Exoccelar     parietal 

6.  Exoccelar      parietal 

cell-layer  of   the 

cell-layer  of    the 

epithelium  of  the 

epithelium  of  the 

body-wall      (also 

body- wall      (also 

ccelom  (also  male 

ccelom  (also  male 

male  germ-plate?) 

male  germ-plate?) 

germ-plate  >) 

germ-plate  ?) 

III.  Producti 

of  the  Differentiation  of  the  Intestinal-fibrous  Layer. 

1.  Body-cavity 

1.  Body-cavity 

1.  Body-cavity 

7.  rieuro-peritoneal 

(Caeloma) 

(Cceloma) 

((uloma) 

cavity 

8.  LndocceUir    outer- 

8. Endoccelar    outer- 

8. Endoccelar  visceral 

8.  Kndoccelar  visceral 

most      cell-layer 

most      cell-layer 

epithelium  of  the 

epithelium  ol  the 

of   the   Intestinal 

of    the   intestinal 

ccelom    (together 

ccelom     (together 

wall        (together 

wall        (together 

with    the  female 

with    the    female 

with  the   female 

with  the   female 

germ-plate  ?) 

germ-plate  ?) 

germ-plate  ?) 

germ-plate  i) 

9.  Dorsal  vessel 

9.  Heart 

9.  Chamber     of    the 
heart  (and   main 
artery) 

9.  Aorta  (primordial) 

10.  Ventral  vessel 

10.  

10.  

10.  Heart     (and     gill- 

11.  Intestinal  wall  (ex- 

11. Intestinal  wall  (rx- 

11.  Intestinal  wall  (ex- 

11. Intestinal  wall  (ex- 

cept  the    epithe- 

cept  the    epithe- 

cept  the  epithe- 

cept   the   epithe- 

lium) 

lium) 

lium) 

lium) 

IV.  Products  of  the  Differentiation  of  the  Intestinal-glandular  Layer. 


12.  Intestinal    epithe 
hum 


12.  Intestinal   epithe- 
lium 


12.  Intestinal    epithe- 
lium 


12.  Intestinal     epithe- 
lium 


CHAPTER  XXV. 

DEVELOPMENT   OP  THE  URINARY   AND   SEXUAL   ORGANS. 

Importance  of  Reproduction. —  Growth. —  Simplest  Forms  of  Asexual  Repro- 
duction :  Division  and  the  Formation  of  Buds  (Gemmation). — Simplest 
Forms  of  Sexual  Reproduction :  Amalgamation  of  Two  Differentiated 
Cells ;  the  Male  Sperm-cell  and  the  Female  Egg-cell. — Fertilization. — 
Source  of  Love. — Original  Hermaphroditism  ;  Later  Separation  of  the 
Sexes  (Gonochorisrn). — Original  Development  of  the  Two  Kinds  of 
Sexual  Cells  from  the  Two  Primary  Germ-layers. — The  Male  Exoderm 
and  Female  Entoderm. — Development  of  the  Testes  and  Ovaries. — 
Passage  of  the  Sexual  Cells  into  the  Ccelom. — Hermaphrodite  Rudiment 
of  the  Embryonic  Epithelium,  or  Sexual  Plate. — Channels  of  Exit,  or 
Sexual  Ducts. — Egg-duct  and  Seed-duct. — Development  of  these  from 
the  Primitive  Kidney  Ducts. — Excretory  Organs  of  Worms. — "  Coiled 
Canals  "  of  Ringed  Worms  (Annelida). — Side  Canals  of  the  Amphioxus. 
— Primitive  Kidneys  of  the  Myxinoides. — Primitive  Kidneys  of  Skulled 
Animals  (Craniota). —  Development  of  the  Permanent  Secondary 
Kidneys  in  Amniota.- — Development  of  the  Urinary  Bladder  from  the 
Allantois. — Differentiation  of  the  Primary  and  Secondary  Primitive 
Kidney  Ducts. — The  Miillerian  Duct  (Egg-duct)  and  the  Wolffian  Duct 
(Seed-duct). — Change  of  Position  of  the  Germ-glands  in  Mammals. — 
Formation  of  the  Egg  in  Mammals  (Graafian  Follicle). — Origin  of  the 
External  Sexual  Organs. — Formation  of  the  Cloaca. — Hermaphroditism 
in  Man. 

"  The  most  important  truths  in  Natural  Science  are  discovered,  neither 
by  the  mere  analysis  of  philosophical  ideas,  nor  by  simple  experience,  but 
by  reflective  experience,  which  distinguishes  the  essential  from  the  accidental 


IMPORTANCE   OF   THE   REPRODUCTIVE   SYSTEM.  389 

in  the  phenomena  observed,  and  thus  finds  principles  from  which  many 
experiences  can  be  derived.  This  is  more  than  mere  experience  ;  it  is, 
so  to  speak,  philosophical  experience." — Johannes  Mulleii  (1810). 

If  we  judge  of  the  importance  of  the  organ-systems  of  the 
animal  body  according  to  the  number  and  variety  of 
phenomena  which  they  present,  and  according  to  the 
physiological  interest  connected  with  them,  we  must  recog- 
nize as  one  of  the  most  important  and  interesting  organic 
systems,  the  one  to  the  development  of  which  we  now, 
finally,  turn ;  the  system  of  the  reproductive  organs.  Just 
as  nutrition  is  the  first  and  most  important  condition  of 
self-preservation  of  the  organic  individual,  so  by  repro- 
duction alone  is  the  preservation  of  the  kind  or  species 
effected,  or,  rather,  the  preservation  of  the  long  series  of 
generations,  which  in  their  genealogical  connection  form  the 
sum  of  the  organic  tribe,  or  phylum.  No  organic  individual 
enjoys  an  eternal  life.  To  each  is  granted  but  a  short 
span  of  time  for  his  individual  evolution,  a  brief,  fleeting 
moment  in  the  long  millions  of  years  of  the  earth's  organic 
history. 

Reproduction  in  connection  with  Heredity  has,  there- 
fore, long  been  regarded  as,  after  nutrition,  the  most 
important  fundamental  function  of  the  organism,  and  it  is 
customary  to  make  this  a  primary  distinction  between 
living  bodies  and  lifeless  or  inorganic  bodies.  But  this 
distinction  is  in  reality  not  so  deep  and  thorough  as  it  at 
first  appears,  and  as  is  generally  assumed.  For,  if  the 
nature  of  the  phenomena  of  reproduction  is  closely  con- 
sidered, it  is  soon  seen  that  it  may  be  reduced  to  a  more 
general  cpuality,  that  of  growth,  which  belongs  to  inorganic, 
as  well  as  to  organic  bodies.     Reproduction  is  a  nutrition 


390  THE    EVOLUTION   OF   MAN. 

and  a  growth  of  the  organism  beyond  the  individual  size, 
which,  therefore,  raises  a  part  of  the  organism  to  the  rank 
of  a  whole  (vol.  i.  p.  159).  This  is  most  clearly  seen  by 
observing  the  reproduction  of  the  simplest  and  lowest 
organisms,  especially  of  the  Monera  (p.  46)  and  of  the  one- 
celled  Amoeba  (p.  48).  In  these,  the  simple  individual  pos- 
sesses only  the  form-value  of  a  single  plastid.  As  soon  as, 
by  continued  nutrition  and  simple  growth,  this  has  reached 
a  certain  size,  it  does  not  exceed  that  size,  but  falls,  by 
simple  division,  into  two  similar  halves.  Each  of  these 
two  halves  thenceforth  leads  an  independent  life,  and  again 
grows,  till,  having  reached  the  same  limit  of  growth,  it  once 
more  divides.  At  each  of  these  simple  self-divisions,  two 
new  central  points  of  attraction  for  the  particles  of  the 
body  are  formed,  as  foundations  of  the  two  new  indi- 
viduals.194 

In  many  other  Primitive  Animals  {Protozoa),  the  simple 
reproduction  is  accomplished,  not  by  division,  but  by  the 
formation  of  buds  (gemmation).  In  this  case,  the  growth, 
which  prepares  the  way  for  reproduction,  is  not  total  (as  in 
the  case  of  division),  but  partial.  Hence  in  the  case  of 
gemmation,  the  product  of  local  growth,  which,  as  a  bud, 
forms  a  new  individual,  can  be  distinguished,  as  a  young 
individual,  from  the  parent-organism  from  which  it 
originates.  The  latter  is  older  and  larger  than  the  former. 
In  the  case  of  division,  on  the  contrary,  the  two  products 
are  of  equal  age  and  of  equal  form-value.  Further 
differentiated  forms  of  asexual  reproduction,  connected 
with  gemmation,  are,  thirdly,  the  formation  of  germ-buds, 
and,  fourthly,  the  formation  of  germ-cells.  The  latter, 
however,  brings  us  directly  to  sexual  reproduction,  for  which 


RUDIMENTARY   REPRODUCTIVE   SYSTEM.  39 1 

the  opposed  differentiation  of  the  two  sexes  is  the  condition. 
In  my  Generelle  Morphologie  (vol.  ii.  pp.  32-71),  and  in 
my  "  Natural  History  of  Creation  "  (vol.  i.  p.  18-3),  I 
have  fully  discussed  the  connection  of  these  various  forms 
of  reproduction. 

None  of  the  earliest  ancestors  of  Man  and  of  the  higher 
animals  were  capable  of  the  higher  function  of  sexual 
reproduction,  but  multiplied  only  in  an  asexual  manner,  by 
division  or  gemmation,  by  the  formation  of  germ-buds,  or  of 
germ-cells,  as  is  still  the  case  with  most  Primasval  Animals 
or  Protozoa.  It  was  not  until  a  later  period  in  the  organic 
history  of  the  earth,  that  sexual  difference  of  the  two 
sexes  could  arise  ;  and  this  took  place  at  first  in  the 
simplest  manner  by  the  severance  of  two  cells  which 
amalgamated  from  the  community  of  the  many-celled 
organism.  We  may  say  that,  in  this  case,  growth,  which  is 
the  condition  necessary  to  reproduction,  was  attained  by 
the  union  of  two  full-grown  cells  into  a  single  cell  which 
then  exceeded  its  proper  size  ("copulation"  or  conjuga- 
tion"). At  first,  the  two  united  cells  may  have  been 
entirely  alike.  Soon,  however,  by  natural  selection,  a  con- 
trast must  have  arisen  between  them.  For  it  must  have 
been  very  advantageous  to  the  newly-created  individual  in 
the  struggle  for  existence,  to  have  inherited  various  quali- 
ties from  the  two  parent-cells.  The  complete  development 
of  this  progressive  contrast  between  the  two  producing 
cells,  led  to  sexual  differentiation.  One  cell  became  a 
female  egg-cell,  the  other,  a  male  seed  or  sperm  cell. 

The  simplest  form  of  sexual  reproduction  among  existing 

animals,  is  exhibited  in  Gastraeads  and  the  lower  Sponges, 

especially  the  Chalk  Sponges,  and,  also,  in   the  simplest 
40 


392  THE   EVOLUTION   OF   MAN. 

Hydroid  Polyps.  In  the  Haliphysema  (Fig.  315)  and  in 
the  Olynthus  the  whole  body  is  a  simple  intestinal  pouch, 
which  is  only  essentially  distinguished  from  the  gastrula  by 
the  fact  that  it  is  adherent  by  the  end  opposite  the  mouth. 
The  thin  wall  of  the  pouch  consists  only  of  the  two 
primary  germ-layers.  As  soon  as  it  is  sexually  mature, 
single  cells  of  the  wall  become  female  egg-cells,  others 
become  male  sperm-cells,  or  seed-cells ;  the  former  grow 
very  large,  as  they  form  a  considerable  number  of  yelk- 
granules  in  their  protoplasm  (Fig.  181,  e);  the  latter,  on  the 
contrary,  by  continued  division,  become  very  small,  and 
modify  into  movable  "pin-shaped"  spermatozoa  (Fig.  17, 
vol.  i.  p.  173).  Both  kinds  of  cells  sever  themselves  from  their 
birthplace,  the  primary  germ-layers,  fall  either  into  the 
surrounding  water  or  into  the  intestinal  cavity,  and  there 
unite  by  amalgamation.  This  is  the  very  important  process 
of  the  fertilization  of  the  egg-cell  by  the  sperm-cell.  (Cf. 
Fig.  18,  vol.  i.  p.  175.) 

These  simplest  processes  of  sexual  reproduction,  as 
exhibited  at  the  present  time  in  the  lowest  Plant  Animals, 
especially  in  the  Chalk  Sponges  and  Hydroid  Polyps,  inform 
us  of  several  extremely  important  and  significant  facts ; 
in  the  first  place,  we  learn,  that  for  sexual  reproduction  in 
its  simplest  form,  nothing  more  is  required  than  the 
blending  or  amalgamation  of  two  differing  cells,  a  female 
er-o--cell  and  a  male  sperm-cell,  or  seed-cell.  All  other 
circumstances,  and  all  the  other  extremely  complex  pheno- 
mena, accompanying  the  act  of  sexual  reproduction  in  the 
higher  animals,  are  of  a  subordinate  and  secondary  charac- 
ter, and  have  only  attached  themselves  secondarily  to  that 
simplest  primary  process  of  copulation  or  fertilization,  or 


RELATION   OF   THE   SEXES. 


393 


have  arisen  by  differentiation.  But,  now,  if  we  consider 
what  an  extraordinarily  important  part  is  everywhere 
played  by  the  relation  of  the  two  sexes  in  organic  nature, 
in  the  vegetable  kingdom,  as  in  animal 
and  human  life;  how  the  reciprocal 
inclination  and  attraction  of  the  sexes, 
love,  gives  the  impetus  of  the  most 
varied  and  remarkable  processes,  is, 
even,  one  of  the  most  important 
mechanical  causes  of  the  highest 
differentiation  in  life  ; — if  we  consider 
this,  we  cannot  over-estimate  this  re- 
tracing of  "  love "  to  its  primitive 
source,  to  the  power  of  attraction  be- 
tween two  differing  cells.  Every- 
where   throughout    animated    nature 


Fig.  315. — Longitudinal  section  through  a 
Haliphyscma  (Gastnvada).  The  egg-cells  (e)  are 
enlarged  epithelial  cells  of  the  entoderm  (rj), 
and  lie  freely  in  the  primitive  intestinal  cavity 
(d):  m,  mouth-opening  ;  h,exoderm. 


the  greatest  results  proceed  from  this  most  insignificant 
cause.  It  is  only  necessary  to  think  of  the  part  played  in 
nature  by  the  flowers,  the  reproductive  organ  of  flowering 
plants ;  or  of  the  multitude  of  wonderful  phenomena 
caused  by  sexual  selection  in  animal  life;  or,  finally,  of  the 
important  influence  exerted  by  love  on  human  life  :  the  coa- 
lescence of  two  cells  is  everywhere  the  single,  original 
impelling  motive ;  everywhere  this  apparently  trivial  pro- 


394  THE   EVOLUTION   OF   MAX. 

cess  exerts  the  greatest  influence  on  the  development  of  the 
most  varied  circumstances.  We  may,  indeed,  assert,  that 
no  other  organic  process  can  be,  even  remotely,  compared  to 
this  in  extent  and  intensity  of  differentiating  effect.  For 
is  not  the  Semitic  myth  of  Eve,  who  seduced  Adam  to 
knowledge,  and  is  not  the  old  Greek  legend  of  Paris  and 
Helen,  and  are  not  very  many  other  famous  fictions,  merely 
the  poetical  expression  of  the  immeasurable  influence,  which 
love,  in  connection  with  "  sexual  selection,"  36  has  exerted, 
ever  since  the  differentiation  of  the  two  sexes,  on  the  pro- 
gress of  the  world's  history  ?  All  other  passions  that  agitate 
the  human  breast  are  in  their  combined  effects  far  less 
powerful  than  love,  which  inflames  the  senses  and  fools  the 
understanding.  On  the  one  hand,  we  gratefully  glorify  love 
as  the  source  of  the  most  splendid  creations  of  art ;  of  the 
noblest  productions  of  poetry,  of  plastic  art  and  of  music  ; 
we  reverence  in  it  the  most  powerful  factor  in  human 
civilization,  the  basis  of  family  life,  and,  consequently,  of 
the  development  of  the  state.  On  the  other  hand,  we  fear 
in  it  the  devoui'ing  flame  which  drives  the  unfortunate  to 
ruin,  and  which  has  caused  more  misery,  vice,  and  crime, 
than  all  the  other  evils  of  the  human  race  taken  together. 
So  wonderful  is  love,  and  so  immeasurably  important  is  its 
influence  on  mental  life,  on  the  most  varied  functions  of  the 
medullary  tube,  that  in  this  point,  more  than  in  any  other, 
"  supernatural "  causation  seems  to  mock  every  natural 
explanation.  And  yet,  notwithstanding  all  this,  the  com- 
parative history  of  evolution  leads  us  back  very  clearly  and 
indubitably  to  the  oldest  and  simplest  source  of  love,  to 
the  elective  affinity  of  two  differing  cells :  the  sperm-cell 
and  the  e£r£-cell. 


HERMAPHRODITISM.  395 

Just  as  the  lowest  Plant  Animals  exhibit  this  most 
simple  origin  of  the  complex  phenomena  of  reproduction, 
so,  in  the  second  place,  they  reveal  the  highly  important 
fact,  that  the  earliest  and  most  primitive  sexual  relation 
was  hermaphroditism,  and  that  the  separation  of  the  sexes 
originated  from  this  only  secondarily  (by  division  of  labour). 
Hermaphroditism  is  prevalent  in  lower  animals  of  the  most 
different  groups;  in  these,  each  single  individual,  when 
sexually  mature,  each  person,  contains  male  and  female 
sexual  cells,  and  is,  therefore,  capable  of  self-fertilization 
and  self-reproduction.  Thus,  not  only  in  the  lowest  Plant 
Animals  just  mentioned  (the  Gastmeads,  Chalk-sponges, 
and  many  Hydroid  Polyps)  do  we  find  egg-cells  and 
sperm-cells  united  in  one  and  the  same  person ;  but 
many  Worms  (for  example,  the  Ascidians,  Earth  Worms 
and  Leeches),  many  Snails  (the  common  garden  Snail),  and 
many  other  invertebrate  animals  are  also  hermaphrodite. 
All  the  earlier  invertebrate  ancestors  of  man,  from  the 
Gastraeada  up  to  the  Chordoma,  must  also  have  been  her- 
maphrodite. So,  probably,  were  also  the  earliest  Skulled 
Animals  (Figs.  52-5G,  e,  h,  vol.  i.  p.  25C).  One  extremely 
weighty  piece  of  evidence  of  this  is  afforded  by  the  remark- 
able fact,  that  even  in  Vertebrates,  in  Man  as  well  as  other 
Vertebrates,  the  original  rudiment  of  the  sexual  organs  is 
hermaphrodite.  The  separation  of  the  sexes  (Gonoclio- 
ri&tth),  the  assignment  of  the  two  kinds  of  sexual  cells 
to  different  individuals,  originated  from  hermaphroditism 
only  in  the  farther  course  of  tribal  history.  At  first,  male 
and  female  individuals  differed  only  in  the  possession  of  the 
two  kinds  of  cells,  but  in  other  respects  were  exactly  alike, 
as  is  now  the  case  in  the  Amphioxus  and  the  Cyclostoina. 


396  THE   EVOLUTION    OF   MAN. 

Not  until  a  later  period,  by  the  law  of  sexual  selection,  so 
brilliantly  elucidated  by  Darwin,  were  developed  the  so- 
called  "  secondary  sexual  characters,"  that  is,  those  dif- 
ferences in  the  male  and  female  sexes  which  are  exhibited, 
not  in  the  sexual  organs  themselves,  but  in  other  parts  of 
the  body  (for  example,  the  beard  of  the  man,  the  breast  of 
the  woman).36 

The  third  important  fact,  taught  us  by  the  lower  Plant 
Animals,  refers  to  the  earliest  origin  of  the  two  kinds  of 
sexual  cells.  For,  as  in  Gastrseads,  and  in  many  Sponges  and 
Hydroids,  in  which  we  meet  with  the  simplest  rudiments 
of  sexual  differentiation,  the  whole  body  consists  throughout 
life  only  of  the  two  primary  germ-layers,  the  two  kinds  of 
sexual  cells  can,  therefore,  only  have  originated  from  cells 
of  the  two  primary  germ-layers.  This  simple  discovery  is 
of  extreme  importance,  because  the  question  of  the  first 
origin  of  the  egg-cells  as  well  as  of  the  sperm-cells  in  the 
higher  animals — and  especially  in  Vertebrates — presents 
unusual  difficulties.  In  these  animals  it  usually  appears 
as  if  the  sexual  cells  developed,  not  from  one  of  the  two 
primary,  but  from  one  of  the  four  secondary  germ-layers. 
If,  as  most  authors  assume,  they  do  originate  from  the 
middle-layer,  or  mesoderm,  the  fact  is  due  to  an  ontogenetic 
heterotopism,  to  a  displacement  in  position.  (Cf.  vol.  i.  p.  13.) 
Unless  the  unjustifiable  and  paradoxical  assumption,  that 
the  sexual  cells  are  of  entirely  different  origin  in  the  higher 
and  in  the  lower  animals,  is  accepted,  we  are  compelled  to 
derive  them  originally  (phylogenetically),  in  the  former  as  in 
the  latter,  from  one  of  the  two  primary  germ-layers.  It  must 
then  be  assumed  that  these  cells  of  the  skin-layer  or  of 
the  intestinal  layer,  which  must  be  regarded  as  the  earliest 


ORIGIN   OF   THE   SEXUAL   CELLS.  397 

progenitors  of  the  sperm-cells  and  of  the  egg-cells,  with- 
drew, during  the  separation  of  the  skin-fibrous  layer  from 
the  skin-sensory  layer,  or  of  the  intestinal-fibrous  layer 
from  the  intestinal-glandular  layer,  into  the  body-cavity 
cceloma),  which  was  in  process  of  formation;  and  that 
they  thus  acquired  the  internal  position  between  the  two 
fibrous  layers,  which  appears  as  their  original  position, 
when  the  sexual  cells  first  become  distinct  in  the  vertebrate 
embryo.  Otherwise,  we  should  be  obliged  to  accept  the 
improbable  polyphyletic  hypothesis,  that  the  origin  of  the 
e<™-cells  and  sperm-cells  is  different  in  the  higher  and  in 
the  lower  animals,  that  their  origin  in  the  former  is  inde- 
pendent of  that  in  the  latter. 

If  we,  accordingly,  derive  the  two  kinds  of  sexual  cells 
from  the  two  primary  germ-layers  in  man  as  in  all  other 
animals,  the  farther  question  arises  :    Did  the  female  egg- 
cells  and  the  male   sperm-cells  develop  from  both  primary 
germ-layers,  or  from  one  only  ?  and,  in  the  latter  case,  from 
which  of  the  two  ?    This  important  and  interesting  question 
is  one  of  the  most  difficult  and  obscure  problems  in  the 
history  of  evolution,  and,  up  to  the  present  moment,  no  full 
and   clear  solution  has    been  attained.     On  the    contrary, 
the   most   opposite  answers  are   given  to  it  even  yet  by 
naturalists  of  note.     Among  the  various  possible  solutions 
only   two   have   been   generally  considered.     It   has   been 
supposed    that  both  kinds   of   sexual   cells   originally  de- 
veloped from  the  same  primary  germ-layer,  cither  from  the 
skin-layer  or  the  intestinal  layer  ;  but  almost  as  many  and 
as  able  observers  have  accepted  the  one  as  the  origin  as 
the  other.     Quite  recently  the   Belgian  naturalist,  Eduard 
van  Beneden,  has  asserted,  on  the  contrary,  that  the  egg-cells 


398  THE   EVOLUTION   OF   MAN. 

originate  from  the  intestinal  layer,  the  sperm-cells  from  the 
skin-layer.195  In  Gastrseads,  Sponges,  and  Hydro-medusae 
this  appears  really  to  be  the  case.  The  development  of  the 
sexual  differences,  which  is  so  rich  in  results,  must,  ac- 
cordingly, have  commenced  even  during  the  differentiation 
of  the  two  primary  germ-layers  in  the  simplest  and  lowest 
Plant  Animals  ;  the  exoderm  would  be  the  male  germ-layer, 
the  entoderm,  the  female.  If  this  discovery  of  Van  Beneden 
is  established  and  proves  to  be  a  universal  law,  Biology  will 
gain  a  most  pregnant  advance ;  for  not  only  would  all  the 
contradictory  empiric  explanations  be  answered,  but  a  new 
path  would  be  opened  for  philosophic  reflection  on  one  of 
the  most  important  of  biogenetic  processes. 

If  we  now  trace  the  Phylogeny  of  the  sexual  organs 
in  our  earliest  Metazoic  ancestors  further,  as  it  is  indicated, 
at  the  present  time,  in  the  Comparative  Anatomy  and 
Ontogeny  of  the  lowest  Worms  and  Plant  Animals,  we 
note,  as  the  first  advance,  the  accumulation  of  the  cells  of 
both  sexes  into  definite  groups.  While  in  Sponges  and 
the  lowest  Hydra-Polyps  single  scattered  cells  separate  from 
the  cell-layers  of  the  two  primary  germ-layers,  and  become 
isolated  and  free  sexual  cells,  in  the  higher  Plant  Animals 
and  Worms  we  find  these  same  cells  associated  and  col- 
lected into  groups  of  aggregate  cells,  which  are,  hence- 
forward, called  "  sexual  glands,"  or  "  germ-glands  "  (gonades). 
It  is  only  now  that  we  can  speak  of  sexual  organs  in  the 
morphological  sense.  The  female  germ-glands  which,  as 
such,  in  their  simplest  form  constitute  a  mass  of  homo- 
genous egg-cells,  are  the  ovaries  (ovaria,  or  oophora ;  Fig. 
211,  e,  p.  198).  The  male  germ-glands,  which  in  then- 
primitive  form  also  consist  merely  of  a  mass  of  sperm-cells, 


DEVELOPMENT  OF  THE  SEXUAL  ORGANS.      399 

are  the  testes  (testiculi,  or  ore?/ ides;  Fig.  211,  h).  We  find 
the  ovaries  and  testes  in  this  earliest  and  simplest  shape 
not  only  in  many  Worms  {Annelida)  and  Plant  Animals, 
but  also  in  the  lowest  Vertebrates,  in  the  Skull-less  Animals 
(Acrania).  In  the  anatomy  of  the  Amphioxus  we  found  the 
ovaries  of  the  female  and  the  testes  of  the  male  consisting 
of  twenty  to  thirty  elliptic  or  roundly  four-cornered  simple 
sacs,  of  small  size,  attached  to  the  inside  of  the  gill-cavity 
on  each  side  of  the  intestine.     (Cf.  vol.  i.  p.  425.) 

Only  a  single  pair  of  germ-glands,  lying  far  down  in  the 
floor  of  the  body-cavity  (Fig.  316,  g),  exist  in  all  Skull,,! 
Animals  (On  n  lota).  The  first  traces  of  these  appear  in  the 
ccelom-epithelium.  Probably,  in  this  case  also,  the  male 
sperm-cells  originate  from  the  skin-layer,  the  female  egg- 
cells,  on  the  contrary,  from  the  intestinal  layer.  The  earliest 
traces  are  visible  in  the  einbryo  at  the  point  where  the 
skin-fibrous  layer  and  the  intestinal-fibrous  layer  meet  in 
the  middle  plate  (mesentery-plate)  (Fig.  318,  mp,  p.  408). 
At  this  very  important  point  in  the  ccelom-wall,  where  the 
endoccelar  (or  visceral  ccelom-epithelium)  merges  into  the 
exocoelar  (or  parietal  ccelom-epithelium),  in  the  embryo  of 
.Man  and  the  other  Skulled  Animals  a  small  aggregation  of 
cells  becomes  visible,  at  a  very  early  period,  and  this,  accord- 
ing to  Waldeyer,1^  we  may  call  the  "  germ-epithelium,"  or 
(corresponding  with  the  other  plate-shaped  rudiments  of 
organs)  the  sexual  plate  (Fig.  31G,#;  Plate  IV.  Fig.  5, /,•;.  The 
cells  of  this  germ-plate,  or  sexual  plate  (lamella  sexual  is)  are 
essentially  distinguished  by  their  cylindrical  form  and  by 
their  chemical  constitution  from  the  other  cells  of  the 
ccelom;  they  are  of  quite  different  significance  from  the  flat 
cells   of    the   "serous    ccelom-epithelium"  which   line   the 


4-00 


THE    EVOLUTION   OF   MAN. 


remainder  of  the  body-cavity  (cceloma).  Of  these  latter— 
the  true  ccelom-cells— those  which  invest  the  intestinal 
tube  and  the  mesentery  ("  endocmlar  ")  originate  from  the 


Fig  316  —Transverse  section  through  the  pelvic  region  and  the  hind 
limbs  of  an  embryo  Chick  in  the  fonrth  day  of  incubation,  enlarged  about 
40  times:  h,  horn-plate;  w,  medullary  tube;  n,  canal  of  the  medullary 
tube  •  u,  primitive  kidneys  ;  x,  notochord;  e,  hind  limbs  ;  b,  allantois  canal 
in  ventral  wall ;  t,  aorta ;  v,  cardinal  veins  ;  a,  intestine ;  d,  intestinal- 
glandular  layer;  /,  intestinal-fibrous  layer ;  g,,  germ-epithelium ;  r,  dorsal 
muscles ;  c,  body-cavity,  or  Ccelom.     (After  Waldeyer.) 

intestinal-fibrous  layer  (in  Fig.  5,  Plate  IV.,  coloured  red) ; 
those  which  line  the  inner  surface  of  the  external  Avail  of 
the  abdomen  ("  exoccelar  ")  are,  on  the  contrary,  the  product 
of  the  skin-fibrous  layer  (coloured  blue  in  Fig.  5,  Plate  IV.) ; 
but  the  sexual  cells  which  make  their  appearance  at  the 
boundary  line  between  the  two  forms  of  ccelom-cells,  and 


DIFFERENTIATION    OF   THE   SEXES.  4OI 

which  insert  themselves,  to  a  certain  extent,  between  the 
endoccelar  and  the  exoccelar,  there  forming  the  germ- 
plate,  cannot  be  referred  either  to  the  intestinal-fibrous 
layer  or  to  the  skin-fibrous  layer,  but  directly  to  the  two 
primary  germ-layers;  for  there  are  important  grounds  for 
supposing  that  even  the  first  rudiment  of  the  sexual  plate  is, 
probably,  hermaphroditic,  and  that  this  "  sexual  epithelium  " 
(visible,  in  Man  and  ail  other  Vertebrates,  between  the  exo- 
ccelar  and  the  endoccelar)  represents  a  primaeval  and  simple 
hermaphrodite  gland.  (Cf.  vol.  i.  p.  25G,  Figs.  52-56,  e,  h.) 
The  inner  half  of  this,  in  contact  with  the  intestinal-fibrous 
layer,  which  is  derived  from  the  intestinal-glandular  layer, 
would  be  the  rudiment  of  the  ovary ;  its  outer  half,  in 
contact  with  the  skin-fibrous  layer,  which  originates  from 
the  intestinal-glandular  layer,  would  be  the  rudiment  of  the 
testes.     This  is,  of  course,  only  conjectural. 

We  ought,  accordingly,  to  distinguish  two  different 
sexual  plates  or  germ-epithelia ;  the  female  sexual  plate,  a 
product  of  the  intestinal  layer,  which  gives  rise  to  the 
ovary-epithelium — the  mother  cells  of  the  ova  ("ovary- 
plate");  and  the  male  sexual  plate,  lying  externally  over  the 
former,  and  which  is  a  product  of  the  skin-layer,  from  which 
originates  the  testes-epithelium — the  mother  cells  of  the 
sperm-threads  ("  testes-plate ") ;  but  even  the  first  recog- 
nizable rudiments  of  the  two  sexual  plates  appear,  indeed, 
so  intimately  associated  in  the  human  embryo  and  in  those 
of  the  higher  Vertebrates,  that  hitherto  they  have  been  re- 
garded as  a  single,  undifferentiated,  common  rudiment  of  an 
organ  ;  and  it  is  still  possible  that  the  two  kinds  of  sexual 
glands  arise  by  secondary  differentiation  from  a  common 
rudiment. 


4-02  THE   EVOLUTION   OF   MAN. 

Though  we  must  recognize  the  formation  of  the  two 
kinds  of  sexual  cells,  and  in  their  union  at  fertilization  as 
the  one  essential  act  of  sexual  reproduction,  yet,  in  the  great 
majority  of  animals,  other  organs  exist  which  also  take 
part  in  the  act  of  fertilization.  The  most  important  of 
these  secondary  sexual  organs  are  the  exit-ducts  which 
serve  to  conduct  the  mature  sexual  cells  out  of  the  body, 
and,  next  to  these,  the  copulative  organs,  which  transmit 
the  fertilizing  sperm  from  the  male  person  to  the  female, 
in  which  the  eggs  are  situated.  These  latter  organs  exist 
only  in  the  higher  animals  of  various  tribes,  and  are  far  less 
widely  distributed  than  the  exit-ducts.  Even  these  latter, 
however,  are  only  of  secondary  formation,  and  are  wanting 
in  many  animals  of  the  lower  groups.  In  these,  as  a  rule, 
the  mature  sexual  cells  are  simply  ejected  from  the  body. 
In  some  cases  they  pass  out  directly  through  the  outer 
skin-covering  (as  in  the  Hydra  and  many  of  the  Hy- 
droidea) ;  in  other  cases,  they  enter  the  stomach-cavity, 
and  are  ejected  through  the  mouth-opening  (in  Gastrseads, 
Sponges,  and  other  Hydroid  Polypes  and  Coral  Animals) ; 
in  yet  other  cases,  they  enter  the  body-cavity  and 
pass  out  through  a  special  aperture  in  the  ventral  wall 
(jjorus  genitalis).  The  latter  is  the  case  in  many  Worms 
and  even  in  a  few  lower  Vertebrates  (Cyclostoma  and 
a  few  Fishes).  These  indicate  the  earliest  condition  of 
this  matter  as  it  was  in  our  ancestors.  On  the  other 
hand,  in  all  higher,  and  most  lower  Vertebrates  (as  also 
in  most  higher  Invertebrates)  special  tube-shaped  exit- 
ducts  from  the  sexual  cells,  or  sexual  ducts  (gonophori), 
are  present  in  both  sexes.  In  the  female  these  convey  the 
egg-cells  out  from  the  ovaries,  and  hence  they  have  been 


EGG- DUCTS   AND   SPERM-DUCTS.  403 

called  egg-ducts  (piriductus,  or  tubes  fallopice).  In  the 
male  sex  these  tubes  convey  the  sperm-cells  from  the  testes, 
and  hence  they  are  called  sperm-ducts  (spevmacluctus,  or 
vasa  deferentia). 

The  original,  genetic  condition  of  these  two  outlets 
is  exactly  the  same  in  Man  as  in  all  higher  Vertebrates, 
while  in  most  Invertebrates  it  is  entirely  different ;  for 
while  in  the  latter  the  sexual  ducts  develop  directly  from 
the  sexual  glands,  or  from  the  external  skin,  or  from  the  in- 
testinal canal,  in  Vertebrates  an  organ-system  is  employed 
for  the  conveyance  of  the  sexual  products ;  one  which  origin- 
ally had  a  very  different  significance  and  function — the 
kidney  system,  or  urinary  organs.  The  original,  primary  func- 
tion of  these  organs  is  simply  to  eliminate  useless  matter 
from  the  body  in  a  liquid  form.  The  liquid  product  of  this 
secretion  is  called  the  urine,  and  is  discharged  either  directly 
through  the  external  skin,  or  through  the  last  section  of  the 
intestine.  The  tube-shaped  "  urinary  ducts  "  only  second- 
arily absorb  the  sexual  products  also  and  convey  them  out ; 
they  thus  become  "  urogenital  ducts  "  (ductus  urogenitales). 
This  remarkable  secondary  combination  of  the  urinary  and 
the  sexual  organs  into  a  common  "  urogenital  apparatus,"  or 
"  urogenital  system,"  is  highly  characteristic  of  the  higher 
Vertebrates.  In  the  lowest  of  these  it  is,  however,  wanting, 
while,  on  the  other  hand,  it  is  found  in  the  higher  Ringed 
Worms  (Annelida).  To  estimate  this  rightly,  we  must  first 
•dance  at  the  comparative  economy  of  the  urinary  organs 
as  a  whole. 

The  kidney  system  or  urinary  system  (syst&ma  uro- 
poeticam)  is  one  of  the  earliest  and  most  important  organ- 
s}rstems  in  the  differentiated  animal  body,  as  has  already 


404  THE    EVOLUTION   OF   MAN. 

been  incidentally  mentioned.  (Cf.  Chapter  XVII.)  It  is 
found  almost  universally  distributed,  not  only  in  the  higher 
animal  tribes,  but  even  in  the  more  primitive  Worm  tribe. 
Anions'  the  latter  it  even  occurs  in  the  lowest  and  most 
imperfect  known  Worms — the  Flat  Worms  (Plathehninthes) 
(Fig.  181,  nc,  p.  80).  Although  these  accelomatous  Worms 
have  no  body-cavity,  no  blood,  no  vascular  system,  they 
always  have  a  kidney  system.  It  consists  of  a  pair  of 
simple  or  of  branched  canals,  lined  by  a  layer  of  cells,  which 
absorb  useless  juices  from  the  tissues  and  discharge  thorn 
through  an  external  skin-opening  (Fig.  184,  nm).  Not 
only  the  free-living  Gliding  Worms  (Turbellaria),  but  also 
the  parasitic  Sucking  Worms  (Trematoda),  and  even  the 
still  more  degraded  Tape  Worms,  which,  in  consequence 
of  their  parasitic  habit  of  life,  have  lost  their  intestinal 
canal,  are  all  provided  with  these  "  kidney  canals  "  or  primi- 
tive kidneys.  Usually  these  canals  in  the  Worms  are  called 
excretory  organs,  and  in  former  times  they  used  to  be  called 
water-vessels.  Phylogenetically  they  must  be  regarded  as 
highly-developed  pouch-like  skin-glands  resembling  the 
sweat-glands  of  Mammals,  and,  like  these,  developed  from 
the  skin-sensory  layer.  (Cf.  Fig.  210,  n,  p.  198,  and  Fig.  214, 
p.  202.) 

While  in  these  lowest  unsegmented  Worms  only  a  single 
pair  of  kidney  ducts  is  present,  in  the  higher  segmented 
Worms  these  ducts  exist  in  greater  numbers.  In  Eino-ed 
Worms  {Annelida),  in  which  the  body  is  composed  of  a 
great  number  of  segments,  or  metamera,  a  pair  of  these 
primitive  kidneys  (hence  known  as  segmental  organs,  or 
canals)  exists  in  each  separate  segment.  In  this  case,  also, 
the  canals  are  very  simple  tubes,  which,  on  account  of  their 


THE   PRIMITIVE   KIDNEYS.  405 

coiled  or  looped  form,  are  called  "  coiled  canals."  To  the 
primary,  external  aperture  in  the  outer  skin,  originally 
alone  present,  a  secondary,  internal  aperture  into  the  body- 
cavity  (cosloma)  is  now  added.  This  opening  is  provided 
with  vibratory  cilia,  and  is  thus  enabled  to  absorb  the 
secretional  juices  from  the  body-cavity  and  to  discharge 
them  from  the  body.  Now  in  these  Worms  also  the  sexual 
cells,  which  develop  in  the  simplest  form  upon  the  inner 
surface  of  the  abdominal  wall,  pass,  when  mature,  into  the 
coelom,  are  drawn  into  the  internal,  funnel-shaped  ciliated 
openings  of  the  kidney  canals,  and  are  carried  out  of  the 
body  with  the  urine.  Thus  the  urine-forming  "coiled 
canals,"  or  "  primitive  kidneys,"  serve,  in  the  female  Ringed 
Worms,  as  "  oviducts,"  and,  in  the  male,  as  "  sperm-ducts." 

It  would  of  course  be  most  interesting  to  know  the 
condition,  on  this  point,  of  the  Amphioxus,  which,  standing 
midway  between  Worms  and  Vertebrates,  affords  us  so 
much  valuable  information.  Unfortunately  this  animal, 
for  the  present,  affords  no  solution  of  this  matter.  At 
present  we  know  nothing  certainly  as  to  the  relation 
between  the  urinary  and  the  sexual  organs  of  the  Amphi- 
oxus. Some  zoologists  assert  that  this  animal  has  no 
kidneys ;  others  regard  the  two  long  "  side  canals "  as 
atrophied  primitive  kidney  ducts  (Fig.  152,  S,  vol.  i.  p.  423)  ; 
yet  others  consider  certain  glandular  epidermis-swellings  on 
the  inner  surface  of  the  gill-cavity  to  be  rudimentary  kidneys. 
Most  probably,  a  great  reversion  has  affected  the  original 
primitive  kidney  canals  in  the  Amphioxus,  amounting  per- 
haps to  their  entire  phylogenetic  loss. 

Very  interesting  inferences   may    be    drawn    from    the 
Vertebrates  of  the  next  stage — the  Monorhina,  or  Cyclos- 


406 


THE   EVOLUTION   OF  MAN. 


toma.     Although  both  orders  of  this  class— the  Myxinoides 
as   well    as  the   Petromyzontes — possess  developed,    urine- 
secreting  kidneys,  these  organs  do  not  in  this  case  serve  to 
carry  away  the  sexual  cells.     These  cells  pass  directly  from 
the  germ-glands  into  the  coelom,  and  are  discharged  through 
a  posterior  aperture  in  the  abdomen.     The  condition  of  the 
primitive  kidneys  in  these  is,  however,  very  interesting,  and 
throws  light  on  the  complex  kidney 
structure  of  the  higher  Vertebrates. 
In  the  first    place,     in  the   Myxi- 
noides (Bclellostoma)  we  find  a  long 
tube,    the    primitive    kidney    duct 
tproturetcr,    Fig.  317,  a),   on    each 
side.       This    opens    internally    into 
the  coelom  through  a  ciliated  funnel- 
shaped     aperture     (as    in     Ringed 
Worms);  it  opens  externally  through 
an  opening  in  the  outer   skin.     A 
great    number  of  small  horizontal 
tubes  ("  segmental  canals,"  or  primi- 

Fig.  317.— A.  Portion  of  kidney  of  Bdel- 
lostoma :  a,  primitive  kidney  duct  (protu- 
reter);  b,  segmental  canals,  or  primitive 
urine  canals  (tubuli  wrvniferi) ;  c,  kidney, 
vesicles  (capsulce  Malphigiana''). — B.  Por- 
tion of  the  same,  much  enlarged  :  c,  kidney- 
vesicle,  with,  the  ylomerulus  ;  d,  approaching 
artery  ;  e,  retreating  artery.  (After  Johannes 
Muller.) 


tive    urine    tubes)    open  on  its  inner  side.     Each  of  these 
terminates    in  a   blind,   vesicular   capsule  (c)   enclosing   a 


THE    PRIMITIVE   KIDNEY   OF   SKULLED   ANIMALS.        407 

knot  of  blood-vessels  (glomerulus,  an  arterial  net,  Fig. 
oV7,B,c).  Afferent  arterial  branches  (vasa  afferentia)  con- 
vey arterial  blood  into  the  coiled  branches  of  the  "glome- 
rulus" (d),  and  efferent  arterial  branches  (vasa  efferentia) 
again  cany  it  out  of  the  glomerulus  (e). 

In  Primitive  Fishes  (Selachii)  also  there  is  a  longitudi- 
nal series  of  segmental  canals,  which  open  outwardly  in 
the  primitive  kidney  ducts.  The  segmental  canals  (a  pair 
in  each  metameron  of  the  central  part  of  the  body)  open,  in 
this  case,  freely  into  the  body-cavity,  through  a  ciliated 
funnel  (as  in  Ringed  Worms,  or  Annelids).  A  part  of  this 
organ  forms  a  compact  primitive  kidney,  while  the  rest  is 
employed  in  the  formation  of  the  sexual  organs. 

The  primitive  kidney  in  the  embryo  of  Man  and  in  that 
of  all  other  Skulled  Animals  (Craniota)  is  first  formed  in 
the  same  simple  shape  which  persists  throughout  life  in 
Myxinoides,  and  partly  in  Selachii.  We  found  this  primi- 
tive organ  in  the  human  embryo  at  that  early  period  just 
succeeding  the  separation  in  the  skin-sensory  layer,  of  the 
medullary  tube  from  the  horn-plate,  and  the  differentiation, 
in  the  skin-fibrous  layer,  of  the  notochord,  the  primitive 
vertebral  plate,  and  the  skin-muscle  plate.  As  the  first 
rudiment  of  the  primordial  kidneys,  a  long  thin,  thread-like 
string  of  cells,  which  is  soon  hollowed  out  into  a  canal, 
appears  in  this  case,  on  each  side,  immediately  below  the 
horn-plate ;  this  extends  in  a  straight  line  from  front  to 
back,  and  is  plainly  seen  in  the  cross  section  of  the  embryo 
Fig.  318)  in  its  original  position  in  the  space  between  the 
horn-plate  (A),  the  primitive  vertebrae  (uw),  and  the  skin- 
muscle  plate  (hpl).  The  first  origin  of  this  primitive 
kidney  duct  is  still  a  matter  of  dispute,  some  ontogenists 


408  THE   EVOLUTION   OF  MAN. 

referring  it  to  the  horn-plate,  others  to  the  primitive  ver- 
tebral plate,  and  yet  others  to  the  skin-muscle  plate.  Pro- 
bably its  earliest  (phylogenetic)  origin  is  to  be  found  in  the 
skin-sensory  layer ;    but  it  very  soon  quits  its  superficial 


>r9 


Fig.  318. — Transverse  section  through  the  embryo  of  a  Chick,  on  the 
second  day  of  incubation  :  h,  horn-plate  ;  m,  medullary  tube  ;  ung,  primitive 
kidney  duct ;  ch,  notochord ;  uw,  primitive  vertebral  cord  ;  hpl,  skin- 
fibrous  layer;  df,  intestinal-fibrous  layer;  mp,  mesentery-plate,  or  middle 
plate  (point  of  attachment  of  the  two  fibrous  layers) ;  sp,  body-cavity 
(coeloma);  ao,  primitive  aorta;  dd,  intestinal-glandular  layer.  (After 
Kolliker.) 

position,  passes  inward,  between  the  primitive  vertebral 
plates  and  the  side  plates,  and  finally  lies  upon  the  inner 
surface  of  the  body-cavity.  (Cf.  Figs.  66-69,  u,  vol.  i.  p.  277, 
and  Figs.  95-98,  p.  319;  also  Plate  IV.  Figs.  3-6,  u.)  While 
the  primitive  kidney  duct  is  thus  making  its  way  inward, 
on  its  inner  and  under  side  appear  a  large  number  of  small 
horizontal  tubes  (Fig.  319,  a),  exactly  corresponding  to  the 
segmental  canals  of  the  Myxinoides  (Fig.  317,  b).  Like  the 
latter,  these  are,  probably,  originally  protuberances  of  the 
primitive  kidney  ducts  (Fig.  316,  u).  At  the  blind,  inner 
end  of  each  of  the  primitive  urinary  tubes  an  arterial 
glomerulus  is  formed,  which  grows  into  this  blind  end 
from  within,  forming  a  "vascular  coil."  The  glomerulus 
to  a  certain  extent  expands  the  bladder-like  blind  end 
of  the  small  urinary  tubes.    As  the  primitive  urinary  tubes, 


RUDIMENTARY    PRIMITIVE   KIDNEYS. 


409 


which  are,  at  first,  very  short,  grow  longer  and  broader, 
each  of  the  two  primitive  kidneys  assumes  the  form  of  a 
semi-pinnate  leaf  (Fig.  320).     The  urinary  tubes  (u)  repre- 


b    r     b 


Fig.  319. — Rudimentary  primitive  kidney  of  embryonic  Dog.  The  pos- 
terior portion  of  the  body  of  the  embryo  is  seen  from  the  ventral  side, 
covered  by  the  intestinal  layer  of  the  yelk-sac,  which  has  been  torn  away, 
and  thrown  back  in  front  in  order  to  show  the  primitive  kidney  ducts  with 
the  primitive  kidney  tubes  (a)  :  b,  primitive  vertebras ;  e,  dorsal  medulla  ; 
d,  passage  into  the  pelvic  intestinal  cavity.     (After  Bischoff.) 

Fig.  320. — Primitive  kidney  of  a  human  embryo:  u,  the  urine-tubes  of 
the  primitive  kidney;  »■,  Wolffian  duct;  w',  upper  end  of  the  latter  (Mnr- 
gagni's  hydatid)  ;  m,  Mullerian  duet ;  i»',  upper  end  of  the  latter  (Fallopian 
hydatid)  ;  g,  hermaphrodite  gland.     (After  Kobelt.) 


sent  the  tissue  and  the  primitive  kidney  duct  (w)  the 
mid-rib.  On  the  inner  margin  of  the  primitive  kidney  the 
rudiment    of    the    hermaphrodite    sexual     gland     already 


410  THE  EVOLUTION   OF  MAN. 

appears  as  a  body  of  considerable  size.  The  posterior  end 
of  the  primitive  kidney  duct  opens  into  the  lower  extremity 
of  the  last  section  of  the  rectum,  so  that  this  organ  becomes 
a  cloaca.  But  this  opening  of  the  primitive  kidney  duct 
into  the  intestinal  canal  must  be  regarded,  phylogenetically, 
as  a  secondary  condition.  Originally,  as  is  indicated  clearly 
in  the  Cyclostoma,  they  issued  through  the  external  abdo- 
minal skin,  quite  independently  of  the  intestinal  canal,  thus 
proving  their  early  phylogenetic  origin  from  the  horn-plate, 
as  outer  skin  glands. 

While  in  the  Myxinoides  the  primitive  kidneys  per- 
manently retain  this  simple  form,  as  they  do  partially  in 
Primitive  Fishes  (Selachii),  in  all  other  Craniota  it  appears 
only  temporally  in  the  embryo,  as  the  ontogenetic  repro- 
duction of  the  primordial  phylogenetic  condition.  In  these 
Skulled  Animals  the  primitive  kidney,  by  vigorous  growth, 
increases  in  length,  and  by  the  increase  in  number  and  the 
coiling  of  the  urinary  tubes,  very  soon  assumes  the  form  of 
a  large  compact  gland,  of  oblong,  oval,  or  spindle-shaped 
form,  which  extends  longitudinally  through  the  greater 
part  of  the  body-cavity  (coeloma)  of  the  embryo  (Figs.  123,m, 
124,  m,  vol.  i.  p.  370).  In  this  case,  it  lies  near  the  middle  line, 
directly  under  the  primitive  vertebral  column,  and  extends 
from  the  region  of  the  heart  to  the  cloaca.  The  right  and 
left  primitive  kidneys  lie  parallel  and  close  together,  being 
separated  only  by  the  mesentery,  that  narrow,  thin  lamella 
which  connects  the  central  intestine  with  the  lower  surface 
of  the  primitive  vertebral  column.  The  excretory  duct  of 
each  primitive  kidney,  the  protureter,  traverses  the  lower 
and  outer  side  of  the  gland  in  a  posterior  direction,  and 
opens  into  the  cloaca,  close  to  the  root  of  the  allantois ;  at 


WOLFFIAN   BODIES.  4 1 1 

a  later  period,  it  opens  into  the  allantois  itself  (Fig.  136,  0, 
vol.  i.  p.  381). 

The  primitive  kidney  (primordial  kidney)  in  the  embryo 
of  Amniota  was  formerly  called  the  "  Wolffian  body,"  also 
the  "  Okenian  body."  In  all  cases  it  acts  for  a  time  as  a 
true  kidne}r,  draining  and  secreting  the  useless  fluids  of  the 
embryonic  body,  and  discharging  them  into  the  cloaca  and 
then  into  the  allantois.  The  "  primitive  urine  "  collects  in 
the  latter  organ,  and  hence  the  allantois  in  the  embryo  of 
man  and  of  the  other  Amniota  acts  as  a  real  urinary  bladder, 
or  "  primitive  urinary  sac  ; "  yet  it  is  in  no  way  geneti- 
cally connected  with  the  primitive  kidneys,  but  is  rather, 
as  we  have  already  seen,  a  pouch-like  protuberance  of  the  an- 
terior wall  of  the  terminal  intestine  (Fig.  135,  u,  vol.  i.  p.  380), 
The  allantois  is,  therefore,  a  product  of  the  intestinal  layer, 
while  the  primitive  kidneys  are  a  product  of  the  skin- 
laj^er.  Phylogenetically  we  must  conceive  that  the  allan- 
tois originated  as  a  pouch-shaped  protuberance  of  the 
cloacal  wall  resulting  from  the  distension  caused  by  the 
collection  in  the  cloaca  of  the  primitive  urine  secreted 
by  the  primordial  kidneys.  It  is,  originally,  a  blind  sac 
belonging  to  the  rectum  (Plate  V.  Fig.  15,  lib).  The  true 
urinary  bladder  of  Vertebrates,  evidently,  first  appeared  in 
Dipneusta  (in  the  Lepidosiren),  and  was  thence  transmitted, 
first  to  the  Amphibia,  and  then  to  the  Amniota.  In  the 
embryo  of  the  latter  it  protrudes  far  out  of  the  yet  unclosed 
abdominal  wall.  Many  Fishes,  indeed,  also  possess  a  so- 
called  urinary  bladder.  But  this  is  merely  a  local  disten- 
sion in  the  lower  section  of  the  primitive  kidney  ducts, 
and  hence,  both  in  origin  and  in  constitution,  is  essentially 
distinct  from  the  true  urinary  bladder.    The  two  structures 


412  THE  EVOLUTION   OF   MAN. 

are  only  physiologically  comparable ;  they  are,  therefore, 
analogous,  as  having  the  same  function;  morphologically, 
however,  they  are  not  to  be  compared,  or  are  not  homo- 
logous.188 The  false  urinary  bladder  in  Fishes  is  a  pro- 
duct of  the  primitive  kidney  duct,  therefore  of  the  skin- 
layer  ;  the  true  urinary  bladder  in  Dipneusta,  Amphi- 
bia, and  Amniota  is,  on  the  contrary,  a  blind-sac  of  the 
terminal  intestine,  and  hence  a  product  of  the  intestinal 
layer. 

In  all  low  Skulled  Animals  (Craniota),  without  amnion 
(in  Cyclostoma,  Fishes,  Dipneusta,  and  Amphibia),  the 
urinary  organs  remain  in  an  inferior  stage  of  development, 
in  so  far  as  the  primitive  kidneys  (protonephra),  though 
much  modified,  here  act  permanently  as  urine-secreting 
glands.  In  the  three  higher  vertebrate  classes,  included  in 
the  term  Amnion  Animals,  on  the  contrary,  this  is  the  case 
only  for  a  short  period  during  early  embryonic  life.  The 
permanent,  or  secondary  kidneys  (renes,  or  metanephra), 
which  are  peculiar  to  these  three  classes,  are  very  early 
developed.  These  originate,  not  (as  was  long  believed,  on 
the  authority  of  Kemak)  as  entirely  new,  independent- 
glands  of  the  intestinal  tube,  but  from  the  posterior  section 
of  the  primitive  kidney  duct  (prot  ureter).  From  the  latter, 
near  where  it  opens  into  the  cloaca,  a  simple  pouch — the 
secondary  kidney  duct — grows  out,  and  this  increases  con- 
siderably in  length  forwards;  from  the  blind,  upper,  or 
anterior  portion  of  this  the  permanent  kidney  originates, 
precisely  as  the  primitive  kidney  originates  from  the  pri- 
mitive kidney  duct.  The  secondary  kidney  duct  gives  rise 
to  a  number  of  small  blind  tubes — the  secondary  urinary 
tubes  —  and    the    blind     capsule-shaped    ends     of    these 


THE  SECONDARY  KIDNEYS.  413 

are  occupied  by  vascular  coils  (glomeruli).  The  further 
growth  of  these  tubes  results  in  the  compact  secondary 
kidney,  which,  in  Man  and  most  higher  Mammals,  acquires 
the  well-known  bean-like  form ;  in  the  lower  Mammalia, 
in  Birds  and  in  Reptiles,  on  the  other  hand,  it  is  separated 
into  several  lobes.  The  lower,  or  posterior  part  of  the 
permanent  kidney  duct  retains  the  form  of  a  simple  canal, 
widens,  and  thus  forms  the  permanent  urine  duct  (ureter). 
At  first  this  canal,  yet  united  with  the  last  section  of  the 
primitive  kidney  duct,  discharges  into  the  cloaca ;  at  a 
later  period,  it  separates  from  the  primitive  kidney  duct, 
and  yet  later  from  the  rectum,  and  then  it  discharges  into 
the  permanent  urinary  bladder  (vesica  urinaria).  The 
latter  originates  from  the  posterior,  or  lower  part  of  the 
stalk  of  the  allantois  (urachus),  which  widens  and  becomes 
spindle-shaped  before  opening  into  the  cloaca.  The  anterior, 
or  upper  part  of  the  allantois-stalk,  which  passes  in  the 
abdominal  wall  of  the  embryo  to  the  navel,  afterwards 
disappears,  a  useless  cord-shaped  remnant  alone  remaining 
as  a  rudimentary  organ :  this  is  the  single  urinary-bladder 
navel-cord  (ligamentum  vesico-umbilicale  medium).  On 
the  right  and  left  of  this,  in  the  adult  Man,  there  are  two 
other  rudimentary  organs:  the  lateral  urinary -bladder  navel- 
cords  (ligamenta  vesico-umbiliealia  lateralia).  These  are 
the  obsolete  cord-like  remnant  of  the  former  navel-arteries 
(arteries  wmbilicales,  vol.  i.  p.  400;  Fig.  326,  a). 

Although  in  Man,  as  in  all  other  Amnion  Animals,  the 
primitive  kidneys  are  thus  very  early  displaced  by  the 
secondary  kidneys,  and  although  the  latter  alone  afterwards 
act  as  urinary  organs,  the  former  are  not,  however,  alto- 
gether discarded.   Indeed,  the  primitive  kidney  ducts  acquire 


414 


THE   EVOLUTION   OF   MAN. 


a  high  physiological  significance,  as  they  modify  into  ex- 
cretory ducts  of  the  sexual  glands.  In  all  Aniphirhina  or 
Gnathostomi — therefore  in  all  Vertebrates  from  Fishes  up 
to  Man — at  a  very  early  period,  a  second  similar  canal 
appears  in  the  embryo  at  the  side  of  each  primitive  kidney 
duct.  This  canal  is  commonly  called,  after  its  discoverer, 
Johannes  Miiller,  "  Muller's  duct "  {ductus  Millleri),  while 
the  earlier,  primitive  kidney  duct  is  distinguished  as  the 
"  Wolffian  duct "  (ductus  Woljfjii).  The  actual  origin  of 
Muller's  duct  is  still  undetermined ;  Comparative  Anatomy 
and  Ontogeny  seem,  however,  to  indicate  that  it  proceeds 
by  differentiation  from  the  Wolffian  duct.  It  is,  probably, 
most  correct  to  say,  that  the  original  (primary)  primitive 
kidney  duct  breaks  up  by  differentiation  (or  fission)  into 
two  secondary,  similar  ducts;   these  are  the  Wolffian  and 


Fig.  321. — Primitive  kidneys  and  rudiments  of  the  sexual  organs.  A  and 
B,  of  Amphibia  (Frog  larvre)  ;  A,  earlier,  B,  later  condition.  C,  of  a  Mam- 
mal (embryo  of  Ox)  :  u,  primitive  kidneys ;  fc,  sexual  glands  (rudiments  of 
testes  and  ovaries).  The  primary  primitive  kidney  duct  (ug  in  Fig.  A) 
separates  (in  B  and  C)  into  the  two  secondary  primitive  kidney  ducts  ;  the 
Miillerian  duct  (m)  and  the  Wolffian  duct  (ug'),  which  unite  behind  into  a 
genital  cord  (</) ;   I,  groin-cord  of  the  primitive  kidneys.    (After  Gegenbaur.) 


DEVELOPMENT   OF   THE   WOLFFIAN    DUCTS. 


415 


the  Miillerian  ducts.  The  latter  (Fig.  320,  w)  lies  imme- 
diately inside  the  former  (Fig.  320  m).  Both  open  pos- 
teriorly into  the  cloaca. 

Obscure  and  uncertain  as 
is  the  origin  of  the  Miillerian 
and  Wolffian  ducts,  their  later 
history  is  clear  and  definite. 
In  all  Double-nost rilled  (Am- 
phirhina)  and  Jaw-mouthed 
(Gnathostomi)  animals,  from 
Primitive  Fishes  up  to  Man, 
the  Wolffian  duct  becomes  the 
seed-duct,  and  the  Miillerian 
duct,  the  oviduct.  In  each 
sex  only  one  of  these  is  per- 

Fios.  322,  323. — Urinary  and  sexual 
organs  of  an  Amphibian  (Water- Newt, 
or  Triton).  Fig.  322  (A),  female  ; 
Fig.  323  (B),  male:  r,  primitive  kid- 
ney ;  ov,  ovary ;  od,  egg-duct  and 
Rathke's  duct,  both  formed  from  tbe 
Miillerian  duct ;  w,  primitive  urinary 
duct — acting,  in  man,  also  as  seed- 
duct  (re) — opening  below  into  Wolff's 
duct  (u')  ;  ms,  ovary-mesentery  (mes- 
ovarium).     (After  Gegeubaur.) 

sistent;  the  other  entirely  disappears,  or  leaves  only  a 
remnant  as  a  rudimentary  organ.  In  the  male  sex,  in 
which  the  two  Wolffian  ducts  become  sperm-ducts,  certain 
rudiments  of  the  Miillerian  duct  arc  often  found,  which 
we  will  call  "  Rathke's  canals  "  (Fig.  323,  c).  In  the  female 
sex,  where,  on  the  contrary,  the  two  Miillerian  ducts 
41 


416 


THE    EVOLUTION    OF   MAN. 


become  oviducts,  traces  of  the  Wolffian  ducts  remain,  and 
are  known  as  "  Gartner's  canals." 


11  af  S!iT  J  •  it  SEES****. 


rf  -,; 


Figs.  324-326. — Urinary  and  sexual  organs  of  an  embryonic  Ox.  Fig. 
324,  of  female  embryo  of  1J  inch  in  length  ;  Fig.  325,  of  male  embryo 
of  24  inches  in  length ;  Fig.  326,  of  female  embryo  of  24  inches  in  length  : 
xv,  primitive  kidney ;  wg,  Wolff's  duct ;  m,  Muller's  duct ;  m',  upper  end  of 
he  latter  (opened  at  t") ;  i,  lower  thickened  end  of  the  same  (rudiment 
of  uterus)  ;  g,  genital  cord  ;  h,  testes  {ti,  lower,  h",  upper  testis-cord)  ; 
0,  ovary ;  0',  lower  ovary-cord  ;  i,  groin-cord  of  the  primitive  kidney ; 
d,  diaphragm-cord  of  the  primitive  kidney  ;  n,  permanent  kidneys  (below 
these  the  S-shaped  urine-duct  ;  between  the  two  the  rectum)  ;  v,  urine- 
bladder  ;  a,  navel-artery.     (After  Kolliker.) 


The  most  interesting  facts  in  reference  to  this  remaik- 
able  development  of  the  primitive  kidney  ducts  and  their 
union  with  the  sexual  glands  are  exhibited  in  Amphibia 
(Figs.  321-323).  The  first  rudiment  of  the  primitive  kidney 
ducts   and    their    differentiation    into    the    Mullerian    and 


DEVELOPMENT   OF   THE   HUMAN    KIDNEY.  417 

Wolffian  ducts  is  identical  in  "both  sexes,  as  is  the  case  in 
the  embryos  of  Mammals  (Fig.  321,  G,  Fig.  324).  In  the 
female  Amphibia  the  Mullerian  duct  on  each  side  develops 
into  a  large  ovary  (Fig.  322,  od),  while  the  Wolffian  duct  acts 
permanently  as  a  urinary  duct  (u).  In  the  male,  on  the 
contrary,  the  Mullerian  duct  persists  only  as  a  rudimentary 
organ,  without  functional  significance,  as  Rathke's  canal 
(Fig.  323,  c)  ;  the  Wolffian  duct  serves,  in  this  case  also,  as  a 
urinary  duct,  but  also  as  a  sperm  or  seed  duct,  the  seminal 
tubes  (ve)  from  the  testes  (t)  entering  the  upper  part  of  the 
primitive  kidneys,  and  there  uniting  with  the  urinary  canals. 

In  Mammals  these  conditions,  persistent  in  Amphibia,  are 
rapidly  traversed  by  the  embryo  in  an  early  period  of  its 
development  (Fig.  321,  C).  The  primitive  kidneys,  which 
in  non-amnionate  Vertebrates  persist  throughout  life  as  the 
urine-secretory  organ,  are  superseded  by  the  secondary 
kidneys.  The  actual  primitive  kidneys  disappear  almost 
entirely  in  the  embryo  at  an  early  period,  leaving  but  small 
traces.  In  the  male  Mammal  the  supplementary  testis 
(epididymis)  develops  from  the  upper  part  of  the  primitive 
kidney ;  in  the  female  the  same  part  gives  rise  to  a  useless 
rudimentary  organ,  the  supplementary  ovary  {parovarium). 

In  the  female  Mammal  the  Mullerian  ducts  undergo  very 
considerable  changes.  The  actual  ovaries  develop  only  from 
its  upper  part;  the  lower  part  widens  out  into  a  spindle- 
shaped  pouch,  with  a  thick,  fleshy  wall,  within  which  the 
fertilized  egg  develops  into  the  embryo.  This  pouch  is  the 
womb  (uterus).  At  first  the  two  uteri  are  perfectly 
separate,  and  open  on  each  side  of  the  urine-bladder  (vu) 
into  the  cloaca,  as  is  yet  permanently  the  case  in  the 
lowest  living  Mammals,  the  Beaked  Animals  (0 rnithostoma) ; 


4i8 


THE   EVOLUTION    OF   MAN. 


but  even  in  Pouched  Animals  (Marsupialia)  a  connection 
forms  between  the  two  Miillerian  ducts,  and  in  Placental 
Animals  they  coalesce  below  with  the  rudimentary  Wolffian 

ducts,  forming  with  them  a  single 
"sexual  cord"  (funiculus  geni- 
talis). But  the  original  indepen- 
dence of  the  two  parts  of  the 
uterus,  and  of  the  two  vagina 
canals  which  proceed  out  of  their 
lower  extremities,  persists  in  many 
lower  Placental  Animals,  while  in 
the  higher  members  of  the  same 
group,  these  organs  gradually 
coalesce  to  form  one  single  organ. 

Fig.    327.— Female     sexual    The     process     of     coalescence    ad- 
organs  of   a   Beaked   Animal  Vances    steadily   from    below    (or 

(Ornithorhiinchus,     Figs.     195,     „  ..  . 

196):  o,  ovaries;  t,  oviduct;  from  behind)  upwards  (or  for- 
u,  uterus ;  sug,  urinary  sexual  wards).  While  in  many  Gnawing 
cavity  (smus  urogenital)-,  the  Animals  fR0dentia,  e.g.,  Hares  and 

two  parts   of    the  uterus  open  x  °  ' 

into  this  at  u' ■.  cl,  cloaca.  Squirrels)  two  separate  uteri  open 
(After  Gegenbam.)  jn^Q  ^]ie  vagina  canal  which  has 

already  become  simple,  in  other  Gnawing  Animals,  as  also 
in  Beasts  of  Prey,  Whales,  and  Hoofed  Animals  (Ungulata), 
the  lower  halves  of  the  two  uteri  are  already  coalescent, 
their  upper  halves  (the  so-called  horns,  "comua")  remaining 
distinct  ("  uterus  bicornis  ").  In  Bats  and  Semi-apes  these 
upper  horns  are  very  short,  while  the  unified  lower  part 
becomes  longer.  Finally,  in  Apes,  as  in  Man,  the  cohesion 
of  the  two  parts  is  complete,  one  simple  pear-shaped  uterus- 
pouch  alone  remaining,  and  into  this  the  oviducts  open  on 
each  side. 


POSITION   OF   THE   HUMAN   SEXUAL   ORGANS.  419 

In  the  male  Mammal  also,  a  similar  coalescence  of  the 
lower  portion  of  the  Mullerian  and  Wolffian  ducts  takes 
place.  '  In  this  case  also,  these  ducts  form  a  single  "sexual 
cord"  (Fig.  325,  g),  which  likewise  opens  into  the  original 
urinary  sexual  cavity  (sinus  urogenitalis),  which  develops 
from  the  lower  part  of  the  urinary  bladder  (y).  While, 
however,  in  the  male  Mammal  the  Wolffian  ducts  develop 
into  the  permanent  sperm-ducts,  only  very  slight  traces  of 
the  Mullerian  ducts  remain  as  rudimentary  organs.  The 
most  remarkable  of  these  is  the  "male  uterus"  (litems 
masculinus),  which  originates  from  the  lowest,  coalescent 
portion  of  the  Mullerian  ducts,  and  which  is  homologous 
with  the  female  uterus.  It  forms  a  small  flask-shaped 
vesicle,  entirely  without  physiological  significance,  which 
opens  into  the  urinary  tubes  between  the  two  sperm-ducts 
and  the  prostatic  lobes  (vesicula  prostattca). 

The  internal  sexual  organs  in  Mammals  undergo  very 
peculiar  modifications  in  point  of  position.  At  first  the 
germ-glands,  in  both  sexes,  lie  deep  down  in  the  ventral 
cavity,  on  the  inner  side  of  the  primitive  kidneys  (Figs. 
320,  g,  321,  k),  attached  to  the  vertebral  column  by  a  short 
mesentery  (in  the  male,  the  mesorchium ;  in  the  female, 
raesovarium).  It  is  only,  however,  in  Monotremes  that  this 
original  position  of  the  germ-glands  is  (as  in  lower  Verte- 
tebrates)  permanent.  In  all  other  Mammals  (Marsupials  as 
well  as  Placentals)  these  glands  quit  their  place  of  origin 
and  make  their  way  more  or  less  downward  (or  towards  the 
posterior  extremity),  following  the  course  of  a  cord  which 
extends  from  the  primitive  kidney  to  the  groin  region  of 
the  abdominal  wall.  This  is  the  groin-cord  of  the  primitive 
kidney;  in  the  male,  the  "  Hunterian  guiding-cord"  (guber- 


420 


THE   EVOLUTION    OF   MAN. 


naculum  testis)  (Fig.  328,  M,  gh) ;  in  the  female,  the  round 
uterus-cord  (Fig.  328,  F,r).  In  the  latter  the  ovaries 
migrate  more  or  less  in  the  direction  of  the  small  pelvis,  or 


Fig.  328,  II. 


Fig.  328,  F. 


Fig.  328. — Original  position  of  the  sexual  glands  in  the  abdominal  cavity 
of  the  human  embryo  (of  three  months).  Fig.  328,  M,  male  (natural  size)  : 
h,  testis ;  gh,  the  conducting-cord  of  the  testis ;  wg,  seed-duct ;  b,  urinary 
bladder;  uh,  lower  hollow  vein  (vena  cava);  ?in,  supplementary  kidneys; 
n,  kidneys.  Fig.  328  F,  female  (somewhat  enlarged)  :  r,  round  uterus-cord 
(below  this  the  urine-bladder,  above  it  the  ovary) ;  r,  kidney ;  s,  sup- 
plementary kidney ;  c,  blind-intestine  (cacum) ;  o,  small  net ;  om,  large 
net  (between  the  two  is  the  stomach)  ;  I,  spleen.     (After  Kolliker.) 

even  enter  this.  In  the  male  the  testis  quits  the  abdominal 
cavity  altogether,  passing  through  the  groin-canal,  and 
enters  a  sac-shaped,  distended  fold  of  the  external  skin- 
coverino-.  The  coalescence  of  the  right  and  left  folds 
("  sexual  folds  ")  gives  rise  to  the  testis-sac  (scrotum).  The 
various  Mammals  exhibit  the  various  stages  of  this  migra- 
tion. In  the  Elephant  and  in  Whales  the  testes  descend 
very  little,  and  lie  below  the  kidneys.  In  many  Gnawing 
Animals  (Rodentia)  and  Beasts  of  Prey  (Camaria)  they 
enter  the  groin-canal.  In  most  higher  Mammals  they  pass 
down  through  this  into  the  testis-sac ;  usually  the  walls  of 


EXTERNAL  SEXUAL  ORGANS.  421 

the  groin-canal  coalesce.  When,  however,  this  remains 
open,  the  testes  are  able  to  descend  periodically  (in  the  rutting 
season)  into  the  testis-sac,  returning  again  into  the  abdo- 
minal cavity  {e.g.,  in  Pouched  Animals  or  Marsupialia, 
Gnawing  Animals,  Bats,  etc.). 

Another  peculiarity  of  Mammals  is  the  formation  of  the 

external  sexual  organs  which,  as  copulative  organs,  serve 

to    carry   the   fertilizing   sperm  from    the    male   into  the 

female  organism  in  the  act  of  copulation.     Organs  of  this 

sort  are  altogether  wanting  in  most  lower  Vertebrates.     In 

those  which  are  aquatic  (e.g.,  Acrania,  Cyclostoma,  and  most 

Fishes)  the  eggs  and  sperm  are  simply  discharged  into  the 

water,  and  their  coming  together  is  the  result  of  some  lucky 

accident  which  in  this  way  brings  about  impregnation.     On 

the  other  hand,  in  many  Fishes  and  Amphibia  which  bring 

forth  their  young  alive,  there  is  a  direct  transfer  of  the 

sperm  from  the  male  to  the  female  organism  ;  and  this  is 

the  case  in  all  Amniota  (Reptiles,  Birds,  and  Mammals).     In 

these  animals  the  urinary  and  genital  organs  always  open 

originally  into  the  lower  part  of  the  rectum,  which  thus 

forms  a  "  cloaca  "  (p.  345) ;   but  among  Mammals  the  cloaca 

is  permanent  only  in  the  Beaked  Animals  (Omithostoma), 

which   have,  on  this  account,  been  called  Cloacal  Animals 

(Monotrcma,  Fig.  r>27,  d).     In  all  other  Mammals  a  lateral 

partition  wall  develops  in  the  cloaca  (in  the  human  embryo 

about  the  middle  of  the  third  month),  by  which  the  latter 

is  separated   into   two   cavities      The  urinary  sexual  canal 

passes  into  the  anterior  cavity  (svnus  urogenitalis),  and  it 

is  through  this   cavity  alone  that  the   urinary  and  sexual 

products  are  discharged,  while  the  "anal  cavity,"  which  lies 

behind  it,  serves  merely  to  eject  the  excrement  through  the 


422 


THE   EVOLUTION    OF    MAN. 


anus.  Even  before  the  appearance  of  this  partition,  in  the 
Pouched  Animals  (Marsupialia)  and  Placental  Animals,  a 
conical  papilla — the  sexual  protuberance  (phallus,  Fig.  329, 
A,  e,  B,  e) — rises  on  the  anterior  part  of  the  circumference  of 


2-   s 


D. 


B. 


Fig.  329. — External  sexual  organs  of  the  human  embryo  :  A,  neutral 
germ  (in  the  eighth  week ;  twice  the  natural  size ;  with  cloaca)  ;  B,  neutral 
germ  (in  the  ninth  week ;  twice  the  natural  size ;  anus  distinct  from  the 
urogenital  opening) ;  C,  female  germ  in  the  eleventh  week ;  D,  male  germ 
in  the  fourteenth  week ;  e,  sexual  protuberance  (phallus') ;  f,  sexual  furrow ; 
hi,  sexual  folds ;  r,  Raphe  (point  of  union  of  the  penis  arid  scrotum) ; 
a,  anus;  ng,  urinary  sexual  opening;  n,  navel-cord;  s,  tail.  (After  Ecker.) 
Cf.  Table  XLIV.,  p.  431. 


the  cloaca-opening.  The  apex  of  this  is  swollen  into  a  knob 
(the  "  acorn,"  glans).  On  the  under  side  appears  a  furrow 
(sulcus  genitalis,  f),  and  on  each  side  of  the  latter  a  skin- 
fold, or  sexual  fold  (hi).  The  phallus  is  especially  the  organ 
of  the  "  sexual  sense,"  and  over  it  are  distributed  the  sexual 


FALSE   HERMAPHRODITISM.  423 

nerves  (nervi  pudendi)  -which  are  especially  concerned  in 
producing  the  sexual  sensations  (p.  238).  In  the  male  the 
phallus  develops  into  the  masculine  "penis"  (Fig.  329,  D,  e); 
in  the  female  it  becomes  the  much  smaller  "clitoris"  (Fig. 
329,  G,  e) ;  only  in  some  Apes  (Ateles)  does  this  become  un- 
usually large.  The  "  fore-skin "  (prceputium),  in  both 
sexes,  also  develops  as  a  skin-fold  from  the  anterior  part  of 
the  circumference  of  the  phallus.  In  the  male  sexual  furrow 
the  lower  side  of  the  phallus  receives  the  urogenital 
canal,  and,  as  a  continuation  of  the  latter,  modifies,  by  the 
coalescence  of  its  two  parallel  edges,  into  a  closed  canal — 
the  male  urinary  tube  (urethra).  In  the  female  this  occurs 
only  in  a  few  instances  (in  some  Semi-apes,  Gnawing  Animals 
or  Bodentia,  and  Moles) ;  as  a  rule  the  sexual  furrow  remains 
open  and  its  edges  are  developed  into  the  labia  minora. 
The  labia  majora  of  the  female  develops  from  the  two 
parallel  skin-folds  which  appear  on  each  side  of  the  sexual 
furrow.  In  the  male  these  last  folds  coalesce,  forming  a 
closed  sac,  the  testis-sac  (scrotum).  Occasionally  this 
coalescence  does  not  take  place,  and  the  sexual  furrow  also 
sometimes  remains  open  (hypospadia).  In  these  cases  the 
external  male  genitalia  resemble  the  female,  and  this  phe- 
nomenon has  often  been  mistaken  for  hermaphroditism 
(pseudo-hermaphroditism).197 

From  this  and  other  cases  of  false  "hermaphroditism," 
the  much  less  frequent  cases  of  "true  hermaphroditism"  are 
very  distinct.  This  exists  only  when  the  essential  organs  of 
reproduction,  both  kinds  of  germ-glands,  are  united  in  one 
individual.  Either  an  ovary  is  then  developed  on  the  right, 
and  a  testis  on  the  left  (or  vice  versa) ;  or  testes  and  ovaries 
are    developed    on   both   sides,   one   more,  the   'other  less 


424  THE   LVOLUTION   OF   MAN. 

perfectly.  As  we  have  already  seen  that  the  original 
rudiment  of  the  sexual  organs  is  really  hermaphroditic  in 
all  Vertebrates,  and  that  the  separation  of  the  sexes  is  only 
due  to  a  one-sided  development  of  this  hermaphroditic 
rudiment,  these  remarkable  cases  offer  no  theoretic  diffi- 
culties. They  very  seldom,  however,  occur  in  Man  and  the 
higher  Vertebrates.  On  the  other  hand,  we  find  original 
hermaphroditism  constant  in  some  lower  Vertebrates,  as  in 
some  Fishes  of  the  Perch  kind  (Serranus),  and  in  some 
Amphibia  (Bombinator  and  in  Toads).  In  these  cases,  the  ' 
male  has  usually  a  rudimentary  ovary  at  the  upper  ex- 
tremity of  the  testis  ;  on  the  other  hand,  the  female  has 
sometimes  a  rudimentary  testis,  without  function.  This 
also  occurs  occasionally  in  Carp  and  some  other  Fishes. 
We  have  already  seen  how  the  original  hermaphroditism 
is  maintained  in  the  excretory  ducts,  in  Amphibia. 

In  the  germ-history  of  the  human  urinary  and  sexual 
organs,  the  outlines  of  the  history  of  human  descent  have 
been  faithfully  maintained  up  to  the  present  time.  We  can 
trace  their  development  in  the  human  embryo  step  by  step, 
in  the  same  gradations  as  are  exhibited,  one  after  another, 
in  the  comparison  of  the  urogenitals  in  Acrania,  Cyclostomi, 
Fishes,  Amphibians,  and  then  further,  in  the  series  of 
Mammals,  in  Cloacal  Animals  (Monotr ernes),  Pouched 
Animals  (Marsupialia),  and  the  various  Placental  Animals. 
(Cf.  Table  XLIIL)  All  the  structural  peculiarities  of  the 
urogenitals,  distinguishing  Mammals  from  other  Verte- 
brates, are  also  present  in  Man ;  and  in  all  special  charac- 
teristics the  latter  resembles  the  Apes,  and  especially  the 
Anthropoid  Apes.  As  evidence  that  the  special  peculiarities 
of  Mammals  have  been  transmitted  to  Man,  I  will  finally 


FORMATION   OF   THE   EGGS.  425 

briefly  notice  the  similar  manner  in  which  the  eggs  are 
formed  in  the  ovary.  In  all  Mammals,  the  mature  eggs  arc 
contained  in  peculiar  vesicles,  which,  after  their  discoverer, 
Regner  De  Graaf  (1G77),  are  called  the  Graafian  follicles. 
These  were  formerly  regarded  as  the  actual  eggs,  which 
were,  however,  discovered  by  Baer  within  the  Graafian 
follicles  (vol.  i.  p.  55).  Each  follicle  (Fig.  330,  C)  consists  of  a 
round,  fibrous  capsule,  which  contains  fluid  and  is  coated  by 
several  layers  of  cells.  At  one  point  this  cellular  layer  has 
a  knob-like  enlargement  (C,  b),  and,  there,  surrounds  the 
real  egg  (C,  a).  The  mammalian  ovary  is,  originally,  a  very 
simple  oblong  little  body  (Fig.  320,  g),  formed  only  of 
connective  tissue  and  blood-vessels,  and  surrounded  by  a 
cell-layer  (the  epithelium  of  the  ovary,  or  the  female  germ- 
epithelium).  From  this  epithelium,  cords  of  cells  grow 
inward,  into  the  connective  tissue  or  "  stroma "  of  the 
ovary  (Fig.  330,  A,  b).  Single  cells  of  these  cords  increase 
in  size  and  become  egg-cells  (primitive  eggs,  A,  c) ;  but  the 
greater  number  of  the  cells  remain  small  and  form  an 
enveloping  and  nutritive  cellular  layer  (the  follicle-epi- 
thelium) round  each  egg. 

In  Mammals  the  follicle-epithelium  is  at  first  one- 
layered  (Fig.  330,  B,  1),  afterwards  many-layered  (B,  2).  In 
all  other  Vertebrates,  the  egg-cell  is,  indeed,  enclosed  in  a 
permanent  covering  of  small  cells,  an  egg-follicle  ;  but  only 
in  Mammals  does  fluid  accumulate  between  the  growing 
follicle-cells,  and  thus  extends  the  follicle  into  a  round 
bladder  of  considerable  size,  on  the  inner  wall  of  which 
the  egg  lies  excentrically.  In  this  point,  as  in  his  whole 
Morphology,  Man  unmistakably  indicates  his  descent  from 
Mammals. 


426 


THE   EVOLUTION    OF   MAN. 
6 


^J^MHlptaji 


Fig.  330,  C. 


HISTORICAL   IMPORTANCE   OF   THE   SEXUAL   ORGANS.   427 

Pig.  330.— Development  of  human  ovules  within  the  female  ovary. — A. 
Vertical  section  through  the  ovary  of  a  new-born  female  :  a,  epithelium  of 
the  ovary;  b,  rudiment  of  an  egg-cord  ;  c,  young  eggs  in  the  epithelium  ; 
d,  longer  egg-cord  with  the  follicles  ;  e,  group  of  young  follicles ;  /,  single 
young  follicle  ;  g,  blood-vessels  in  the  connective  tissue  (stroma)  of  the 
ovary.  In  the  cords  the  young  primitive  eggs  can  be  distinguished  from 
the  surrounding  cells  of  the  follicle  by  their  relatively  large  size.  (After 
Waldeyer). — 330,  B.  Two  young  follicles  isolated ;  in  1,  the  cells  of  the 
follicle  form  but  a  single  layer  around  the  young  primitive  egg ;  in  2,  they 
form  a  double  layer ;  in  2,  they  begin  to  form  the  primary  chorion  (a),  or 
the  zona  pcllucida  (vol.  i.  p.  135). — 330,  C.  A  mature  human  Graafian  follicle  : 
a,  the  mature  egg ;  b,  the  surrounding  follicle-cells  ;  c,  the  epithelial  cells  of 
the  follicle ;  d,  the  fibrous  membrane  of  the  follicle ;  e,  its  outer  surface. 

The  entire  natural  history  of  the  human  sexual  organs 
is  one  of  the  branches  of  Anthropology  which  affords  the 
strongest  proofs  of  the  origin  of  the  human  race  from  the 
animal  kingdom.  Each  man,  on  knowing  the  pertinent 
facts,  and  without  prejudice,  judging  these  comparatively, 
can  but  be  convinced  that  he  is  descended  from  lower 
Vertebrates.  The  general,  and  the  more  minute  structure, 
the  activity  and  the  individual  evolution  of  the  sexual 
organs,  is  exactly  the  same  in  Man  as  in  Apes.  This  is  as 
true  of  the  male  as  of  the  female,  of  the  internal  as  of  the 
external  genitalia.  The  differences  in  this  matter  between 
Man  and  the  most  man-like  Apes  are  far  less  than  the 
differences  between  the  various  forms  of  Apes.  As,  how- 
ever, all  Apes  are  undoubtedly  from  a  common  origin,  this 
fact  alone  proves,  with  absolute  certainty,  the  descent  of 
Man  from  Apes. 


(     42S     ) 

TABLE    XLIII. 

Systematic  Survey  of  the  most  Important  Periods  in  the  Phylogen* 
of  the  Urinary  and  Sexual  Organs  of  Man.137 

XLIII.  A.  First  main  division  :  the  sexual  organs  (G)  and  the  urinary 
organs  (U)  are  distinct.  (The  sexual  or  genital  system  (G)  and  the 
excretory  or  urinary  system  act  independently  of  each  other.) 

I.  First  Period  :   Genitals  and  Kidneys  of  Gastrceads. 

G.  Single,  scattered  cells  of  the  entoderm  change  into  egg-cells ;  single, 
scattered  cells  of  the  exoderm  into  sperm-cells. 

U.  Special  urinary  organs  are  as  yet  wholly  wanting.  Secretion  is 
performed  by  the  cells  of  the  exoderm. 

II.  Second  Period :  Genitals  and  Kidneys  of  Primitive  Worms. 

G.  The  egg-cells  of  the  entoderm  gather  into  groups  (ovary -plates) ;  as 
do  the  sperm-cells  of  the  exoderm  (testis-plates). 

U.  A  pair  of  simple  pouch-like  skin-glands  (products  of  the  skin-sensory 
layer)  develop  into  extremely  simple  kidney-canals  (excretory  organs  of  the 
Flat-worms,  Platelminth.es). 

III.  Third  Period:   Genitals  and  Kidneys  of  Scolecida. 

G.  After  the  differentiation  of  the  four  secondary  germ-layers  is  com- 
plete, the  egg-cells  pass  from  the  skin-sensory  layer  into  the  skin-fibrous 
layer ;  the  sperm-cells  also  pass  from  the  intestinal-glandular  layer  into  the 
intestinal-fibrous  layer. 

U.  After  the  formation  of  the  ccelom  is  completed,  the  blind  inner  ends 
of  the  two  kidney-canals  (or  "  primitive  kidney  ducts  ")  open  into  the  body- 
cavity  (coeloma). 

IV.  Fourth  Period :  Genitals  and  Kidneys  of  Chordoma. 

G.  The  groups  of  egg-cells  (ovarial  plates)  and  the  groups  of  sperm-cells 
(testes-plates)  meet  at  the  boundary  between  the  endocoolar  (the  visceral 
intestinal-fibrous  layer  of  the  coslom-epithelium)  and  the  exoccelar  (the 
parietal  skin-fibrous  layer  of  the  ccelom-epithelium),  so  as  to  form  the 
hermaphrodite  glands. 

U.  The  primitive  kidney  ducts  differentiate  into  an  excretory  and  a 
glandular  part. 

V.  Fifth  Period  :  Genitals  and  Kidneys  of  A  crania. 

G.  The  sexes  become  distinct.  In  the  female,  only  the  ovary  is  de- 
veloped ;  in  the  male,  only  the  testes. 

U.  The  primitive  kidney  ducts  remain  simple  (atrophied  in  Amphioxus). 


PIIYLOGENY   OF   URINARY   AND   SEXUAL  ORGANS.       429 

VI.  Sixth  Period  1   Genitals  and  Kidneys  of  Cyclostoma. 

G.  Tho  sexual  glands  (numerous  in  Acrania)  coalesce  into  a  pair. 

U.  The  primitive  kidney  ducts  send  out  lateral  branches  which  acquire 
vascular  coils  {glomeruli)  (the  semi-pinnate  primitive  kidneys  of  Bdello- 
stoma). 

XLIII.  B.  Second  main  division :  the  genital  organs  (G)  and  the  urinary 
organs  (U)  becomo  united.  (The  sexual  system  and  the  urinary  system 
are  united  in  the  "  urogenital  system.") 

VII.  Seventh  Period  :   Urogenitals  of  Primitive  Fishes  (Selachii). 

The  primary  primitive  kidney  duct  differentiates  on  each  side,  forming 
two  secondary  canals  ;  the  Wolffian  duct,  which  develops  into  the  seed-duct, 
and  the  Miillerian  duct,  which  develops  into  the  oviduct.  Both  genital 
ducts  originally  open  behind  the  anus  {Pro selachii). 

VIII.  Eighth  Period  :   Urogenitals  of  Dipneusta. 

A  cloaca  is  formed  by  the  union  of  the  urogenital  opening  and  the  cavity 
of  the  anus.  The  single  urinary  bladder  grows  out  from  the  anterior  wall  of 
the  rectum  (Lepidosiren). 

IX.  Ninth  Period  :   Urogenitals  of  Amphibia. 

From  the  uppermost  part  of  the  primitive  kidney  which  is  in  process  of 
atrophy,  pi'oceeds,  in  the  male  sex,  the  supplementary  testis;  in  the  female 
sex,  the  supplementary  ovary.  The  Wolffian  duct  yet  acts,  in  both  sexes,  as 
a  urinary  canal,  and,  in  the  male,  also  as  the  seed-duct.  The  Miillerian 
duct  acts  in  the  female  sex  as  oviduct ;  in  the  male  it  is  a  rudimentary 
organ  (Kathkc's  duct). 

X.  Tenth  Period  :  Urogenitals  of  Protamnia. 

The  atrophied  primitive  kidney  is  replaced  by  tho  permanent  secondary 
kidney  as  the  urinary  organ.  The  urinary  bladder  grows  out  from  the 
ventral  orifice  of  the  embryo  and  forms  the  allantois.  From  tho  anterior 
wall  of  the  cloaca  grows  the  sexual  protuberance  (phallus),  which,  in  the 
male,  develops  to  the  penis,  in  the  female,  to  the  clitoris. 

XL  Eleventh  Period  :   Urogenitals  of  Monotremes. 

Tho  lower  end  of  the  oviduct  enlarges  on  each  side  to  a  muscular 
uterus. 

XII.  Twelfth  Period:  Urogenitals  of  Marsupialia. 

The  cloaca  is  separated  bj  a  partition  into  an  anterior  urogenital  opening 
apertura  urogenital!*)    ami   a    posterior   anal  opening    (anus).       From    the 


430  THE   EVOLUTION   OF  MAN. 

lower  part  of  the  uterus  the  vagina. canal  passes  out  on  each  side.     The 
ovaries  and  testes  begin  to  move  downward  from  their  place  of  formation. 

XIII.  Thirteenth  Period  :   Urogenitals  of  Semi-apes. 

The  lower  parts  of  the  Miillerian  and  the  Wolffian  ducts  coalesce  into 
a  sexual  cord.  The  coalescence  of  the  two  uteri  at  the  lower  part  gives 
rise  to  the  uterus  bicornis.     A  part  of  the  allantois  becomes  the  placenta. 

XIV.  Fourteenth  Period :   Urogenitals  of  Apes. 

The  two  uteri  coalesce  throughout  their  entire  length,  forming  a  single 
pear-shaped  uterus,  as  in  Man. 


(    43i     ) 


TABLE    XLIY. 

Systematic  Survey  of  the  Homologies  of  the  Sexual  Organs  in  the  two  Sexes 

of  Mammals. 

XLIV.  A.  Homologies  op  TriE  Internal  Sexual  Organs. 


6.  Common  Rudiments  of  the 
Internal  Sexual  Organs. 


M.  Internal  Male  Parts. 


F.  Internal  Female  rarts. 


1.  Stale    germ-gland  (testes-plate 

in  the  embryo,  product  oi'  the 
skin-layer?) 

2.  Female  germ-gland  (ovary-plate, 

product     of     the     intestinal 
layer  ?) 

3.  Wolffian  duct  (lateral  primitive 

kidney  duct) 

4  a.  Miillerian  duct 

(Ductus  M&Ueri,  rmtral  pri- 
mitive kidney  duct) 

4  b.  Upper  part  of  the  Miillerian 
duct 

4  c.  Lower  part  of  the  Miillerian 
duct 

5.  Remnant  of  the  primitive  kidney 

(I'rutonephron,  corpus   Wolf- 
fit) 

6.  Groin  ligament  of  the  primitive 

kidney 

(l.iyamcntum  protoncphroin- 
guinale) 
1.  Sexual  mesentery 

(Meseuterium  sexuale) 


1.  Testis 

(Testis,  or  Orchis) 

2.  (Rudimentary  ovary,  dis- 

appears,— remains      in 
some  Amphibia) 

3.  Seed-duct 

(Spermaductus) 

4  a.  Rathke's  duct  (rudi- 
mentary canal  in 
Amphibia) 

4  6.  llydiUis  Morgagni 

i  c.  Uterus  masculwus 
(Vesica  in  prostalica) 

5.  Supplementary  testes 

(Epididymis) 

6.  Hunterian  guiding-cord 

(G ubernaeulum    Hun- 
teri) 

7.  Testis-mesentery 

(Mesorchium) 


1.  Rudimentary    testis    dis- 

appears,— remains      in 
some  Amphibia 

2.  Ovary 

(Ovarium, or  Oophoron) 

3.  Gartnerian     duct     (rudi- 

mentary canal) 
4  a.  Oviduct 

(Oviductus,     or     Tuba 

Fallopiai) 
4  b.  By  talis  Fallopiw 

4  c.  Uterus,  sheath  (vagina) 

5.  Supplementary  ovary 

(Parovarium) 

6.  Round  uterus-cord 

(Ligami  ntuvn        uteri 

rotuitdum) 

1.  Ovary-mesentery 
(Mesovarium) 


XLIV.  B.  Homologies  of  the  External  Sexual  Organs. 


G.  Common  Rudiments  of  the 
External  Sexual  Organs. 

M.  External  Male  Parts. 

F. 

External  Female  Parts. 

3. 

Sexual  protuberance 
(Phallus) 

8. 

Penis 

8. 

Clitoris 

9. 

Fore-skin 

(  I'm  jiutium) 

9. 

Male  fore-skin 
(/v.i  /allium  penis) 

9. 

Fern  ale  fore-skin 
( I'm  put  in  in  clitoridis) 

10. 

folds 
(Plica  </>  nitdUs) 

10. 

I  estee-sac 
(■Scroti 

10. 

Labiapudendi  mnjures 

11 

between  the  two  sexual 

11. 

Seam  ol  the  testis-sao 

11. 

Female  Vulva 

folds 

1 Raphe  scroti ) 

12 

Sexual    edges    (edges    of 
sexual  furrow  ) 

the 

12. 

Edges     of     the     sexual 
lui  row  coalesce 

12. 

Labia  pudendi  minora 

13 

Urogenital  canal 

13. 

13.  Antechamber  of  the  vagina 

i  sunn  urogenitalis) 

(Urethra) 

(  Vestibulum  vagina) 

11 

Glandular  appendages  of 
urogenital  canal 

the 

14. 

Cow  pel's  glands 

11 

Bartholi'a  glands 

CHAPTER  XXVI 

RESULTS   OF   ANTHROPOGENY. 

Review  of  the  Germ-history  as  given. — Its  Explanation  by  the  Fundamental 
Law  of  Biogeny. — Its  Causal  Relation  to  the  History  of  the  Tribe. — 
Rudimentary  Organs  of  Man. — Dysteleology,  or  the  Doctrine  of  Pur- 
poselessness. — Inheritances  from  Apes. — Man's  Place  in  the  Natural 
System  of  the  Animal  Kingdom.— Man  as  a  Vertebrate  and  a  Mammal. 
— Special  Tribal  Relation  of  Men  and  Apes. — Evidences  regarding  the 
Ape  Question. — The  Catarhina  and  the  Platyrhina. — The  Divine  Origin 
of  Man. — Adam  and  Eve. — History  of  the  Evolution  of  the  Mind. — 
Important  Mental  Differences  within  a  Single  Class  of  Animals. — The 
Mammalian  Mind  and  the  Insect  Mind. — Mind  in  the  Ant  and  in  the 
Scale-louse  [Coccus). — Mind  in  Man  and  in  Ape. — The  Organ  of  Mental 
Activity  :  the  Central  Nervous  System. — The  Ontogeny  and  Phy- 
logeny  of  the  Mind. — The  Monistic  and  Dualistic  Theories  of  the 
Mind. — Heredity  of  the  Mind. — Bearing  of  the  Fundamental  Law  of 
Biogeny  on  Psychology. — Influence  of  Anthropogeny  on  the  Victory  of 
the  Monistic  Philosophy  and  the  Defeat  of  the  Dualistic. — Nature  and 
Spirit. — Natural  Science  and  Spiritual  Science. — Conception  of  the 
World  reformed  by  Anthropogeny. 

"  The  Theory  of  Descent  is  a  general  inductive  law  which  results  with 
absolute  necessity  from  the  comparative  synthesis  of  all  the  phenomena  of 
organic  nature,  and  especially  from  the  threefold  parallel  of  phylogenetic, 
ontogenetic,  and  systematic  evolution.  The  doctrine  that  man  has  de- 
veloped from  lower  Vertebrates,  and  immediately  from  genuine  Apes,  is 
a  special  deductive  conclusion,  which  results  with  absolute  necessity  from 
the  general  inductive  law  of  the  Theory  of  Descent.     This  view  of  '  man's 


SUMMARY.  433 

place  in  nature,'  cannot,  we  believe,  be  made  too  prominent.  If  the  Theory 
of  Descent  is  coi'rect  as  a  whole,  then  the  theory  that  man  has  developed 
from  lower  Vertebrates  is  simply  an  unavoidable  deductive  conclusion  from 
that  general  inductive  law.  Hence,  all  farther  discoveries  which  may  in 
future  enrich  our  knowledge  of  the  phyletic  development  of  man,  can  only 
bo  confirmative  of  special  points  of  that  deduction,  which  rests  on  the 
broadest  inductive  basis." — Generelle  Morphologie  (186G). 

As  we  have  now  traversed  the  wonderful  territory  of 
the  history  of  human  development,  and  learned  its  most 
important  parts,  it  seems  appropriate  that,  at  the  close  of 
our  travels,  we  should  look  back  on  the  road  behind  us, 
and,  on  the  other  hand,  glance  forward  along  the  further 
path  of  knowledge  into  which  our  road  will  lead  in  future. 
We  started  from  the  simplest  facts  of  the  history  of  man's 
individual  development;  ontogenetic  facts  which  can,  at 
any  moment,  be  shown  and  established  by  microscopic  or 
anatomic  research.  The  first  and  most  important  of  these 
ontogenetic  facts  is,  that  every  man,  like  every  other 
animal,  is  at  the  commencement  of  his  individual  existence, 
a  simple  cell.  This  egg-cell  exhibits  precisely  the  same 
structure  and  mode  of  origin  as  that  of  any  other  Mammal. 
From  this  cell  proceeds,  by  repeated  division,  a  many-celled 
body,  the  mulberry-germ  (morula) ;  this  changes  into  a 
cup-germ  (gastrula),  and  this,  again,  into  ah  intestinal 
germ-vesicle  (yastrocysiis).  The  two  distinct  cell-strata 
which  compose  its  wall  are  the  two  primary  germ- 
layers  ;  the  skin-layer  (exodcrma)  and  the  intestinal  layer 
(entodcrma).  This  double-layered  germ-form  is  the  onto- 
genetic  reproduction  of  that  extremely  important  phylo- 
genetic  parent-form  of  all  Intestinal  Animals,  to  which  we 
have  given  the  name  Gastrsea. 

As  the  human  germ,  like  that  of  other  Intestinal  Animals, 


434  THE   EVOLUTION   OF   MAN. 

passes  through  this  gastrula-form,  we  are  enabled  to  trace 
its  phylogenetic  origin  back  to  the  Gastrsea.  By  tracing  the 
germ-history  of  the  two-layered  germ  still  farther,  we  found 
that,  by  fission,  four  secondary  layers  are  produced  from 
the  two  original  germ-layers.  These  have  exactly  the  same 
constitution  and  genetic  significance  in  Man  as  in  all  other 
Vertebrates.  From  the  skin-sensory  layer  develops  the 
outer  skin  (epidermis)  and  the  central  nervous  system,  and, 
probably,  the  kidney  system.  The  skin-fibrous  layer  forms 
the  leather-skin  (corium)  and  the  organs  of  motion  (the 
skeleton  and  muscle  systems).  From  the  intestinal-fibrous 
layer  originates  the  vascular  system  and  the  fleshy  wall  of 
the  intestine.  The  intestinal-glandular  layer,  finally,  forms 
only  the  epithelium,  or  the  inner  cellular  layer  of  the 
intestinal-mucous  membrane  and  of  the  intestinal  glands. 

The  manner  in  which  these  various  organic  systems 
develop  from  the  four  secondary  germ-layers,  is,  from  the 
very  first,  exactly  the  same  in  Man  as  in  all  other  Verte- 
brates. The  germ-history  of  each  separate  organ  afforded 
proof  that  the  human  embryo  takes  exactly  the  same  special 
direction  in  its  differentiation  and  formation,  which,  except 
in  Man,  occurs  only  in  the  other  Vertebrates.  Within  this 
great  animal  tribe  we  then  traced,  step  by  step,  and  stage 
after  stage,  the  farther  development  which  takes  place  in  the 
entire  body  as  well  as  in  all  its  several  parts.  This  higher 
development  takes  place  in  the  human  embryo  in  the  form 
peculiar  to  Mammals.  Finally,  we  saw,  that  even  within 
this  class  the  various  stages  of  phylogenetic  development, 
which  determine  the  natural  classification  of  Mammals, 
correspond  throughout  to  the  various  stages  of  ontogenetic 
formation  through  which  the  human  embryo  passes  in  the 


THE  FUNDAMENTAL   LAW  OF  BIOGENY.  435 

further  course  of  its  development.  We  were  thus  enabled 
to  determine  the  place  of  Man  more  definitely  in  the  system 
of  this  class,  and  accordingly  to  establish  the  nature  of  his 
relation  to  the  various  mammalian  orders. 

The  course  of  reasoning  which  we  adopted  in  explaining 
these  ontogenetic  facts,  was  simply  the  logical  carrying  out 
of  the  fundamental  law  of  Biogeny.  In  so  doing  we  have 
constantly  tried  to  carry  out  the  significant  distinction 
between  palingenetic  and  kenogenetic  phenomena.  Palin- 
genesis, or  "the  history  of  inheritance,"  alone  enabled  us  to 
draw  direct  conclusions  from  observed  germ-forms  as  to  the 
tribal  forms  transmitted  by  heredity.  On  the  other  hand, 
these  conclusions  were  more  or  less  endangered,  wherever 
Kenogenesis,  or  "vitiated  evolution,"  was  introduced  by  new 
adaptations.  The  whole  understanding  of  the  history  of  in- 
dividual evolution  depends  on  the  recognition  of  this  most 
important  relation.  We  stand  here  on  the  border-line  which 
sharply  divides  the  new  from  the  old  method  of  scientific 
investigation,  the  new  from  the  old  conception  of  the  world. 
All  the  results  of  recent  morphological  research  drive  us 
with  irresistible  force  to  the  recognition  of  this  fundamental 
principle  of  Biogeny,  and  of  its  far-reaching  consequences. 
These  are,  it  is  true,  irreconcilable  with  the  customary 
mythological  ideas  of  the  world,  and  with  the  powerful 
prejudices  engrafted  into  us  in  early  youth  by  theosophic 
instruction;  but,  without  this  fundamental  law  of  Biogeny, 
without  the  distinction  between  Palingenesis  and  Keno- 
genesis, and  without  the  Theory  of  Descent,  upon  which 
these  are  based,  we  are  entirely  unable  to  understand  the 
facts  of  organic  development ;  without  these,  we  cannot 
afford  the  faintest  explanation  of  any  part  of  this  great  and 


436  THE   EVOLUTION   OF   MAN. 

wonderful  world  of  phenomena.  But,  if  we  recognize  the 
causal  relation  between  the  development  of  the  germ  and 
that  of  the  tribe,  if  we  recognize  the  true  causal  connection 
of  Ontogeny  and  Phylogeny,  which  is  expressed  in  that  law, 
then  the  wonderful  phenomena  of  Ontogeny  explain  them- 
selves most  simply;  then  the  facts  of  germ-development 
appear  but  the  necessary  mechanical  effects  of  the  develop- 
ment of  the  tribe,  conditioned  by  the  laws  of  Heredity  and 
Adaptation.  The  inter-operation  of  these  laws  among  the 
everywhere-active  influences  of  the  struggle  for  existence, 
— or,  as  we  may  simply  say  with  Darwin,  Natural  Selection, 
— is  amply  sufficient  to  explain  to  us  the  entire  process  of 
germ-history  by  the  history  of  the  tribe.  Darwin's  chief 
merit  lies  in  the  fact,  that  by  the  discovery  of  the  inter- 
action of  the  phenomena  of  Heredity  and  Adaptation,  he 
prepared  the  way  for  a  correct,  logical  understanding  of  the 
history  of  Evolution. 

Among  the  numerous  and  important  evidences  that  we 
have  found  for  the  truth  of  this  view  of  our  development 
history,  I  will  only  call  attention  here  once  more  to  the 
peculiarly  valuable  records  of  creation  afforded  by  Dystele- 
ology,  or  the  doctrine  of  purposelessness,  the  science  dealing 
Avith  rudimentary  organs.  It  is  impossible  to  emphasize 
too  often  and  too  strongly  the  high  morphological  import- 
ance of  those  remarkable  parts  of  the  body,  which  are, 
physiologically,  completely  worthless  and  useless.  In  every 
system  of  organs  we  find,  in  Man  and  in  all  higher  Verte- 
brates, some  of  these  worthless  primaeval  heirlooms,  which 
have  been  inherited  from  our  lower  vertebrate  ancestors. 
Thus,  first,  we  find  on  the  outer  surface  of  the  body  a  scanty 
rudimentary  covering  of  hair,  which  is  thicker  only  on  the 


RUDIMENTARY   ORGANS.  437 

head, in  the  armpits,  and  on  some  other  parts  of  the  body.  The 
short  hairs  on  the  greater  part  of  the  surface  of  our  bodies  are 
entirely  useless,  are  without  any  physiological  significance; 
they  are  the  last  scanty  remains  of  the  much  more  fully 
developed  hairy  covering  of  our  Ape  ancestors  (p.  208).  The 
sense-organs  exhibit  a  series  of  the  most  remarkable  rudimen- 
tary parts.  As  we  have  seen,  the  whole  external  shell  of  the 
ear,  with  its  cartilages,  muscles,  and  membranes,  is,  in  Man, 
a  useless  appendage,  destitute  of  the  physiological  importance 
that  was  formerly,  erroneously,  attributed  to  it.  It  is  the 
atrophied  remnant  of  the  pointed,  freely-moving,  and  much 
more  highly  developed  mammalian  ear,  the  muscles  of  which 
we  retain,  although  we  can  no  longer  use  them  (p.  271). 
Again,  we  found,  at  the  inner  corner  of  the  human  eye,  the 
remarkable  little  crescent-shaped  fold,  which  is  of  no  use  to 
us,  and  is  of  interest  only  as  being  the  last  vestige  of  the 
nictitating  membrane ;  of  that  third  inner  e}relid  which  is 
still  of  great  physiological  importance  in  Sharks  and  many 
Amnion  Animals  (p.  259).  Numerous  and  interesting 
dysteleological  proofs  are  also  afforded  by  the  apparatus  of 
motion,  both  by  the  bony  and  the  muscular  systems.  I 
will  only  cite  the  free,  projecting  tail  of  the  human  embryo, 
and  the  rudimentary  caudal  vertebras  developed  in  the 
latter,  together  with  the  pertinent  muscles ;  this  whole 
organ  is  entirely  useless  to  Man,  but  is  of  great  interest  as 
the  atrophied  remnant  of  the  long  tail  of  our  earlier  Ape 
ancestors,  which  was  composed  of  numerous  vertebrae  and 
muscles  ]>  l'n:>;.  From  these  same  ancestors  we  have  also 
inherited  various  bone-processes  and  muscles,  which  were  of 
great  use  to  them  in  their  climbing  life  among  the  trees,  but 
with  us  have  fallen  out  of  use.    At  various  points  under  the 


438  THE   EVOLUTION   OF  MAN. 

skin  we  also  have  entirely  unused  skin-muscles  ;  vestiges  of 
the  largely  developed  skin-muscles  of  our  lower  mam- 
malian ancestors.  It  was  the  function  of  this  "  panniculus 
carnosus  "  to  contract  and  wrinkle  the  skin,  as  we  may  see 
any  clay  done  by  horses  to  drive  away  flies.  We  still 
possess  an  active  remnant  of  this  great  skin-muscle  in  the 
muscle  of  the  forehead,  by  means  of  which  we  wrinkle  the 
forehead  and  draw  up  the  eyebrows ;  but  we  are  no  longer 
able  to  move  at  will  another  considerable  remnant  of  it,  the 
great  skin-muscle  of  the  neck  (platysma  myoides). 

As  in  these  animal  organ-systems  of  our  body,  so  also  in 
the  vegetative  apparatus,  we  meet  with  many  rudimentary 
organs,  most  of  which  we  have  incidentally  noticed.  I  will 
only  cite  the  remarkable  thyroid  gland  (thyreoidea),  the 
rudiment  of  the  crop  and  the  remnant  of  the  ciliated  groove 
(hypobranchial  groove)  present  in  Chordoma,  Ascidia,  and 
Arcrania,  on  the  lower  part  of  the  gill-body  (pp.  336,  353) ; 
also  the  vermiform  process  of  the  blind-intestine  (caecum) 
(p.  344").  In  the  vascular  system  we  find  many  useless 
ducts,  the  vestiges  of  disused  vessels  which  were  formerly 
active  blood-channels ;  such,  for  instance,  are  the  "  ductus 
Botalli"  between  the  lung-artery  and  the  aorta,  and 
the  "ductus  venosus  Arantii,"  between  the  vena  portcc 
and  vena  cava,  and  many  others.  The  numerous  rudi- 
mentary organs  of  the  urinary  and  sexual  systems  (p.  415) 
are  especially  interesting.  Most  of  these  are  developed  in 
one  sex  and  rudimentary  in  the  other.  Thus,  in  the  male, 
the  seed-ducts  form  from  the  Wolffian  ducts,  of  which  the 
only  traces  remaining  in  the  female  are  the  Gartnerian 
canals.  On  the  other  hand,  from  the  Miillerian  ducts  in  the 
female  are  developed  the  oviducts  and  the  uterus;  while  in 


HISTORICAL  IMPORTANCE  OF  THE  RUDIMENTARY  ORGANS.    439 

the  male,  only  the  lower  extremities-  of  these  ducts  remain, 
forming  the  useless  male  uterus  (vesicvla  prostatica).  In 
the  nipples  and  mammary  glands,  the  male  possesses  other 
rudimentary  organs  which,  as  a  rule,  are  functional  only  in 
the  female  (p.  204). 

A  closer  anatomical  examination  of  the  human  body 
would  bring  to  our  notice  a  number  of  other  rudimentary 
organs,  all  of  which  can  be  explained  only  by  the  Theory  of 
Descent.  They  are  among  the  most  important  evidences  for 
the  truth  of  the  mechanical  theory  of  nature,  and  among  the 
most  overwhelming  proofs  against  the  prevailing  teleological 
ideas  of  creation.  If,  in  accordance  with  this  latter  view,  Man 
and  every  other  organism  had  been  designed  for  his  life- 
purpose  from  the  beginning,  and  had  been  called  into  existence 
by  an  act  of  creation,  the  existence  of  these  rudimentary 
organs  would  be  an  incomprehensible  enigma ;  it  would  be 
impossible  to  understand  why  the  Creator  should  have  laid 
this  useless  burden  on  his  creatures  in  their  life-journey,  so 
arduous  at  the  best.  On  the  other  hand,  lrv  means  of  the 
Theory  of  Descent  we  can  explain  their  existence  in  the 
most  simple  way,  and  say  :  The  rudimentary  organs  arc 
parts  of  the  body,  which,  in  the  course  of  centuries, 
have  gradually  fallen  out  of  use ;  organs  which  performed 
definite  functions  in  our  animal  ancestors,  but  which,  in 
us,  have  lost  their  physiological  importance.  They  have 
become  useless  in  consequence  of  our  adaptation  to  new- 
circumstances,  but  yet  are  transmitted  from  generation  to 
generation  by  heredit}7,  and  have  only  slowly  atrophied. 

Like  these  rudimentary  organs,  so  also  all  the    other 

organs   of    our  body   have   been   transmitted   to   us   from 

Mammals,  and,  immediately,  from  our  Ape  ancestors.     The 
42 


440  THE   EVOLUTION   OF   MAN. 

human  body  includes  no  single  organ  which  is  not  in- 
herited from  Apes  ;  but,  by  means  of  our  fundamental  law 
of  Biogeny,  we  can  trace  the  origin  of  our  several  systems 
of  organs  yet  further  down  to  various  lower  ancestral 
grades.  Thus,  for  instance,  we  can  say  that  we  have 
inherited  the  earliest  organs  of  our  body,  the  outer-skin 
(epidermis)  and  the  intestinal  canal,  from  the  Gastrpeads, 
the  nervous  and  muscular  systems  from  the  lower  Worms 
(Archclminthes),  the  vascular  system,  body-cavity  (cceloma), 
and  blood  from  Soft  Worms  (Scolecida),  the  notochord  and 
the  gill-intestine  from  Chorda  Animals,  the  differentiated 
organs  of  sense  from  the  Cyclostoma,  the  limbs  and  the 
Miillerian  ducts  from  Primitive  Fishes  (Selackii),  and  the  ex- 
ternal reproductive  organs  from  Primitive  Mammals  (Pro- 
mammalia).  When  we  stated  the  "  law  of  the  ontogenetic 
connection  of  systematically  allied  forms,"  and  determined 
the  relative  age  of  the  organs,  we  saw  how  we  could  draw 
such  phylogenetic  conclusions  as  these  from  the  ontogenetic 
succession  of  the  organ-systems  (vol.  i.  p.  390 ;  ii.  357). 

By  the  help  of  this  important  law  and  of  Comparative 
Anatomy,  we  were  also  enabled  to  determine  definitely 
"  man's  place  in  nature,"  or,  as  we  may  say,  to  assign  to 
man  his  position  in  the  system  of  the  animal  kingdom.  It 
is  now  usual,  in  the  more  recent  zoological  systems,  to 
distribute  the  whole  animal  kingdom  into  the  seven  tribes, 
or  phyla,  which  are  again  sub-divided,  in  round  numbers, 
into  about  forty  classes ;  and  these  classes  into  about 
two  hundred  orders.  According  to  his  whole  organization, 
Man  is  undoubtedly,  primarily,  a  member  of  but  a  single 
tribe,  that  of  Vertebrates ;  secondly,  he  is  a  member  of  but 
a  single  class,  that  of  Mammals ;  and,  thirdly,  a  member 


"man's  place  in  nature."  441 

of  but  a  single  order,  that  of  the  Apes.  All  the  character- 
istic peculiarities,  distinguishing  Vertebrates  from  the  other 
six  tribes,  distinguishing  Mammals  from  the  other  forty 
classes,  and  distinguishing  Apes  from  the  remaining  two 
hundred  orders  of  the  animal  kingdom,  are  also  present 
in  Man.  Turn  and  twist  as  we  may,  we  cannot  escape  this 
anatomical  and  systematic  fact.  Quite  recently  this  very 
fact  has  led  to  the  liveliest  discussion,  and  has  occasioned, 
especially,  many  disputes  about  the  specific  anatomical 
relationship  of  Man  to  Apes.  The  most  astounding  views 
on  this  "ape  question,"  or  "pithecoid  theory,"  have  been 
uttered.  It  will  therefore  be  well  to  examine  it  closely 
once  more  at  this  point,  and  to  separate  the  essential  from 
the  non-essential  in  it. 

We  will  start  from  the  undisputed  fact,  that  Man,  at  all 
events, — whether  his  special  blood-relationship  to  Apes  is 
acknowledged  or  denied, — is  a  genuine  Mammal,  is  a  Pla- 
cental  Mammal.  This  fundamental  truth  can  be  so  easily 
proved  at  any  moment  by  investigations  in  Comparative 
Anatomy,  that  it  has  been  unanimously  acknowledged  since 
the  separation  of  the  Placental  from  the  lower  Mammals 
(Pouched  Animals,  or  Marsiqncdia,  and  Beaked  Animals,  or 
Ornithostoma).  But,  from  this,  every  logical  adherent  of 
the  doctrine  of  development  at  once  draws  the  conclusion, 
that  man  is  descended  from  one  and  the  same  common 
parent-form,  together  with  all  other  Placental  Animals,  from 
the  progenitor  of  the  Placentalia,  just  as,  further,  we  must 
necessarily  suppose  a  common  mammalian  ancestral  form 
of  all  the  various  Mammals  {Placentalia),  Pouched  Animals, 
and  Cloacal  Animals  (Monotremata)  ;  but  by  this  the  great, 
all-agitating   main   question   of  man's   place   in  nature   is 


442  THE   EVOLUTION    OF   MAN. 

conclusively  settled,  whether  we  ascribe  to  Man  a  nearer  or 
a  more  remote  relationship  to  Apes.  No  matter  whether 
Man  is,  in  a  phylogenetic  sense,  a  member  of  the  Ape  order 
(or,  if  it  is  preferred,  of  the  Primate  order)  or  not, — in 
any  case,  his  direct  blood-relationship  to  all  other  Mammals, 
and  especially  to  the  Placental  Mammals,  is  established.  It 
may  be  that  the  inter-relations  of  the  various  Mammals 
are  quite  different  from  those  now  hypothetically  assumed ; 
but,  in  any  case,  the  common  descent  of  Man  and  all 
other  Mammals  from  a  common  parent-form  is  indis- 
putable. This  primaeval,  long  since  extinct  parent-form, 
which  probably  developed  during  the  Triassic  Period,  was 
the  monotreme  ancestral  form  of  all  Mammals. 

If  this  fundamental  and  extremely  significant  principle 
is  borne  in  mind,  the  "  ape  question  "  will  appear  to  us 
in  a  wholly  different  light  from  that  in  which  it  is  usually 
presented.  A  little  reflection  will  bring  conviction  that 
this  question  has  not  the  importance  that  has  of  late  been 
attributed  to  it ;  for  the  origin  of  the  human  race  from 
a  series  of  various  mammalian  ancestors,  and  the  historical 
development  of  the  latter  from  an  earlier  series  of  lower 
vertebrate  ancestors,  remains  indubitably  established,  no 
matter  whether  the  genuine  "  Apes "  are  regarded  as  the 
nearest  animal  ancestors  of  the  human  race  or  not.  But, 
it  having  become  habitual  to  lay  the  principal  weight  of 
the  entire  question  of  the  origin  of  man  on  this  very 
"  descent  from  Apes,"  I  find  myself  compelled  to  return 
once  more  to  it  here,  and  to  recall  those  facts  in  Com- 
parative Anatomy  and  Ontogeny,  which  conclusively  settle 
this  "ape  question." 

The   shortest   way    to    the   goal   is   the  one  taken  by 


"  HUXLEY'S   LAW.'  443 

Huxley  in  his  celebrated  work,  which  we  have  so  often 
quoted,  on  the  "Evidences  as  to  Man's  Place  in  Nature," — 
the  way  afforded  by  Comparative  Anatomy  and  Ontogeny. 
We  have  to  compare  objectively  all  the  several  organs  of 
Man  with  the  same  organs  in  the  higher  Apes,  and  then  to 
ascertain  whether  the  differences  between  the  former  and 
the  latter  are  greater  than  the  corresponding  differences 
between  the  higher  and  lower  Apes.  The  indubitable  and 
indisputable  result  of  this  comparative  anatomical  investi- 
gation which  was  conducted  with  the  greatest  candour  and 
accuracy,  was  the  important  law,  which,  in  honour  of  its 
discoverer,  we  have  named  Huxley  s  Law;  namely,  that  the 
physical  differences  between  the  organization  of  Man  and 
that  of  the  most  highly  developed  Apes  known  to  us,  are 
much  smaller  than  the  corresponding  differences  between 
the  higher  and  lower  Apes.  We  might  even  define  this  law 
yet  more  exactly  by  excluding  entirely  the  Platyrhina  or 
American  Apes  as  being  more  remote  relatives,  and  limiting 
our  comparison  to  the  narrower  circle  of  relatives,  the 
Catarhina,  or  Apis  of  the  Old  World.  Even  within  this 
small  group  of  Mammals,  we  found  the  differences  of  struc- 
ture between  the  higher  and  lower  Narrow-nosed  Apes,  for 
example  between  the  Gorilla  and  the  Baboon,  much  greater 
than  the  differences  between  these  Man-like  Apes  and  Man. 
When,  in  addition,  we  now  turn  to  Ontogeny,  and  when  we 
find  there,  according  to  our  "  law  of  the  ontogenetic  con- 
ncction  of  systematically  related  forms,  that  the  embryos  of 
Man  and  of  the  Man-like  Apes,  are  identical  for  a  longer 
period  than  the  embryos  of  the  highest  and  of  the  lowest- 
Apes,  we  are  certainly  obliged  to  bring  ourselves,  whether 
with  a  good  or  a  bad  grace,  to  acknowledge  our  origin  from 


444  THE   EVOLUTION    OF   MAN. 

the  Ape  order.  From  the  facts  exhibited  by  Comparative 
Anatomy,  we  can  undoubtedly  form  in  imagination  an 
approximate  image  of  the  structure  of  our  ancestors  during 
the  older  Tertiary  Period ;  we  may  fill  out  the  details  as  we 
will,  yet  this  image  will  be  a  genuine  Ape,  and  a  true 
Catarhine.  For  Man  has  all  the  physical  characters  dis- 
tinguishing the  Catyrhina  from  the  Platyrhina.  Accord- 
ingly, in  the  mammalian  pedigree,  we  must  derive  the 
human  race  directly  from  the  Catarhine  group,  and  refer 
the  origin  of  Man  to  the  Old  World.  For  the  entire  group 
of  the  Catarhine  Apes  has,  as  yet,  been  confined  to  the  Old 
World,  just  as  the  group  of  the  Platyrhine  Apes  has  been 
limited  to  the  New.  Only  the  earliest  root-form,  that  from 
which  both  groups  sprang,  was  common  to  them ;  probably 
it  originated  from  the  Semi-apes  of  the  Old  World. 

Therefore,  although  it  is  thus  indubitably  established  as 
the  result  of  our  objective  scientific  inquiry,  that  the  human 
race  is  directly  descended  from  the  Apes  of  the  Old  World, 
yet  we  will  once  more  state  emphatically  that  this  signifi- 
cant fact  is  not  of  as  great  importance  to  the  main  question 
of  the  origin  of  Man,  as  is  generally  supposed.  For,  even 
if  we  entirely  ignore  the  fact  or  thrust  it  aside,  this  will 
not  affect  all  that  the  zoological  facts  of  Comparative 
Anatomy  and  the  history  of  development  have  taught  us 
concerning  the  placental  character  of  Man.  These  clearly 
prove  the  common  descent  of  Man  and  the  other  Mammals. 
It  is  evident  also,  that  the  main  question  cannot  be  in  the 
least  evaded  or  set  aside  by  the  statement :  "  Man  is,  indeed, 
a  Mammal ;  but  he  branched  off  from  the  others  quite  at 
the  root  of  the  class,  and  has  no  nearer  relationship  with 
any  other  extant  Mammal."     At  all  events,  the  relationship 


EVOLUTION  AND  SENTIMENT.  445 

is  evidently  more  or  less  close  if  we  comparatively  examine 
the  relation  of  the  Mammalian  class  to  the  remaining  forty 
classes  of  the  animal  kingdom.  All  Mammals,  including 
Man,  are,  at  least,  of  common  origin,  and  it  is  equally 
certain  that  their  common  parent-forms  gradually  developed 
from  a  long  series  of  lower  Vertebrates. 

Feeling,  evidently,  rather  than  understanding,  induces 
most  people  to  combat  the  theory  of  their  "descent  from 
Apes."  It  is  simply  because  the  organism  of  the  Ape  appears 
a  caricature  of  Man,  a  distorted  likeness  of  ourselves  in  a 
not  very  attractive  form,  because  the  customary  aesthetic 
ideas  and  self-glorification  of  Man  are  touched  hy  this  in  so 
sensitive  a  point,  that  most  men  shrink  from  recognizing 
their  descent  from  Apes.  It  seems  much  pleasanter  to  be 
descended  from  a  more  highly  developed,  divine  beino-, 
and  hence,  as  is  well  known,  human  vanity  has,  from  the 
earliest  times,  flattered  itself  by  assuming  the  original 
descent  of  the  race  from  gods  or  demi-gods.  The  church, 
with  that  sophistical  distortion  of  ideas  of  which  she  is 
so  great  an  adept,  has  managed  to  extol  this  ridiculous 
pride  as  Christian  humility  ;  and  those  people  who 
reject  with  haughty  horror  every  suggestion  of  descent 
from  lower  animals,  and  consider  themselves  children  of 
God,  those  very  people  are  exceedingly  fond  of  boasting 
about  their  childlike  humility  of  spirit.  In  most  of  the 
sermons  delivered  against  the  progress  of  the  doctrine 
of  evolution,  human  vanity  and  conceit  play  throughout 
a  prominent  part;  and,  although  we  have  inherited  this 
characteristic  weakness  from  Apes,  yet  we  must  confess  to 
having  developed  it  to  a  degree  of  perfection  which 
completely  overthrows  the  unprejudiced  judgment  of  the 


446  THE    EVOLUTION   OF   MAN. 

"  sound  understanding  of  man."  We  ridicule  the  childish 
follies  occasioned  by  the  pride  of  ancestry  among  the 
nobility,  from  the  splendid  Middle  Ages  down  to  our  own 
time,  and  yet  no  small  portion  of  this  groundless  pride 
of  nobility  lurks  in  a  great  majority  of  men.  Just  as  most 
people  prefer  to  trace  their  pedigree  from  a  decayed  baron 
or,  if  possible,  from  a  celebrated  prince,  rather  than  from 
an  unknown,  humble  peasant,  so  they  prefer  seeing  the  pro- 
genitor of  the  human  race  in  an  Adam  degraded  by  the  Fall, 
rather  than  in  an  Ape  capable  of  higher  development  and 
progress.  It  is  a  matter  of  taste,  and  such  genealogical 
preferences  do  not,  therefore,  admit  of  discussion.  Still  I 
must  confess  that,  personally,  I  am  as  proud  of  my  paternal 
grandfather,  who  was  simply  a  Silesian  peasant,  as  of  my 
maternal  grandfather,  who  raised  himself  from  the  position 
of  a  Rhenish  lawyer  to  the  highest  posts  in  the  council 
of  state.  And  it  is  also  much  more  to  my  individual  taste 
to  be  the  more  highly  developed  descendant  of  a  primaeval 
Ape  ancestor,  who,  in  the  struggle  for  existence,  had  de- 
veloped progressively  from  lower  Mammals,  as  they  from 
still  lower  Vertebrates,  than  the  degraded  descendant  of 
an  Adam,  god-like,  but  debased  by  the  Fall,  who  was  formed 
from  a  clod  of  earth,  and  of  an  Eve,  created  from  a  rib  of 
Adam.  As  regards  this  celebrated  "  rib,"  I  must  here  ex- 
pressly add  as  a  supplement  to  the  history  of  the  develop- 
ment of  the  skeleton,  that  the  number  of  ribs  is  the  same  in 
man  and  in  woman.  In  the  latter  as  well  as  in  the  former, 
the  ribs  originate  from  the  skin-fibrous  layer,  and  are  to  be  re- 
garded phylogenetically  as  lower  or  ventral  vertebne  (p.  285). 
Now  I  certainly  hear  some  one  say :  "  That  may  all  be 
right  and  correct  as  far  as  the  human  body  is  concerned,  and, 


EVOLUTION    OF   THE   MIND.  447 

from  the  facts  presented,  it  is  certainly  no  longer  to  be 
doubted  that  this  lias  actually  developed  gradually,  step  by 
step,  from  the  long  ancestral  series  of  Vertebrates;  but  it  is 
quite  otherwise  with  the  'spirit  of  man,'  with  the  human 
mind,  which  cannot  possibly  have  developed  in  a  similar 
way  from  the  mind  of  lower  Vertebrates."  Let  us  see  if  the 
known  facts  of  Comparative  Anatomy,  Physiology,  and 
Evolution  can  meet  this  grave  objection.  We  shall  best 
gain  firm  ground  from  which  to  start  in  this  matter  by 
comparatively  examining  the  minds  of  the  different  Verte- 
brates. Side  by  side  within  the  various  classes,  orders, 
genera,  and  species  of  Vertebrates,  we  find  so  great  a  variety 
of  vertebral  intellects,  that,  at  first  sight,  one  can  scarcely 
deem  it  possible  that  they  can  all  be  derived  from  the  mind 
of  a  common  "  Primitive  Vertebrate."  First,  there  is  the 
little  Lancelet,  which  has  no  brain  at  all,  but  only  a  simple 
medullary  tube,  the  entire  mental  capacity  remaining  at 
the  very  lowest  grade  occurring  among  Vertebrates.  The 
Cyclostomi,  also,  standing  just  above,  exhibit  a  hardly 
higher  mental  life,  though  they  have  a  brain.  Passing  on  to 
Fishes,  we  find  their  intelligence,  as  is  well  known,  also 
at  a  very  low  point.  Not  until  from  these  we  ascend  to  the 
Amphibia,  is  any  essential  progress  in  mental  development 
observable.  This  is  much  greater  in  Mammals,  although, 
even  here,  in  the  Beaked  Animals  (Ornithostoma),  and  the 
next  higher  class,  the  atupid  Pouched  Animals  (Man  vpials  . 
the  entire  mental  activity  is  still  of  a  very  low  order;  but 
if  we  pass  on  from  these  to  Placental  Animals,  within  this 
multiform  group  we  find  such  numerous  and  important 
steps  in  differentiation  and  improvement,  that  the  mental 
differences  between  the  most  stupid  Placental  Animals  (for 


44§  THE   EVOLUTION   OF   MAN. 

instance,  Sloths  and  Armadillos)  and  the  most  intelligent 
animals  of  the  same  group  (for  instance,.  Dogs  and  Apes), 
seem  much  more  considerable  than  the  intellectual  dif- 
ferences between  those  lowest  Placentals  and  the  Pouched 
Animals,  or  even  the  lower  Vertebrates.  Those  differences 
are,  at  any  rate,  much  more  considerable  than  the  dif- 
ferences in  the  intellectual  life  of  dogs,  apes,  and  men.  And 
yet  all  these  animals  are  allied  members  of  a  single  class.198 

This  fact  is  shown  to  a  yet  more  surprising  degree  in 
the  Comparative  Psychology  of  another  class  of  animals, 
which  is  specially  interesting  for  many  reasons,  that  of 
Insects.  It  is  well  known  that  many  Insects  exhibit  a 
mental  capacity  approximately  as  highly  developed  as  is 
possessed  by  Man  only  of  the  vertebrate  group.  It  is  needless 
to  speak  of  the  celebrated  organized  communities  and  states 
of  Bees  and  Ants ;  every  one  knows  that  very  remarkable 
social  arrangements  occur  among  these,  such  as  occur  in  an 
equal  degree  of  development  only  in  the  higher  races  of 
men,  and  nowhere  else  in  the  animal  kingdom.  I  will  only 
allude  to  the  civil  organization  and  government  among 
Monarchical  bees  and  Republican  ants,  to  their  division 
into  various  orders :  the  queen,  the  drone  nobility,  the 
workers,  the  nurses,  soldiers,  and  so  on.  Among  the  most 
remarkable  phenomena  in  this  extremely  interesting  field  of 
life,  is  certainly  the  cattle-keeping  of  certain  Ants,  which 
tend  plant-lice  for  the  sake  of  their  milk  and  regularly 
collect  their  honey-juice.  Even  more  remarkable  is  the 
slave-holding  of  the  large  red  Ants,  which  steal  the  young 
of  the  small  black  species  and  rear  them  to  slave-labour. 
It  has  long  been  known  that  all  these  civil  and  social 
arrangements  of  the  Ants  were  originated  by  the  systematic 


COMPARATIVE   MENTAL   CAPACITIES.  449 

co-operation  of  numerous  citizens,  understanding  each  other. 
Numerous  observations  have  placed  the  astoundingly  high 
intellectual  development  of  these  little  Articulated  Animals 
beyond  all  doubt.  With  this  let  us  compare,  as  Darwin 
lias  done,  the  intellectual  capacity  of  many  lower,  and, 
especially,  of  many  parasitic,  Insects.  There,  for  example, 
are  the  Scale  Insects  (Coccus)  which,  when  mature,  consist 
of  an  entirely  immovable  shield-shaped  body  attached  to 
the  leaves  of  plants.  Their  feet  are  atrophied.  Their 
mouths  are  embedded  into  the  tissue  of  the  plant,  the 
juices  of  which  they  suck.  The  whole  mental  activity  of 
this  motionless  female  parasite  consists  in  the  enjoyment  it 
derives  from  sucking  these  juices  and  from  sexual  inter- 
course with  the  unattached  male.  The  same  is  true  of  the 
maggot-like  female  of  the  Twisted-wings  (Strepsiptera), 
which  spends  its  whole  life,  wingless  and  footless,  as  a 
motionless  parasite  in  the  body  of  the  wasp.  There  can  be 
no  suspicion  of  any  higher  mental  activity  there.  If  these 
brutish  parasites  are  compared  with  the  mentally  active 
and  sensible  ants,  it  will  certainly  be  admitted,  that  the 
psychical  differences  between  the  two  are  much  greater 
than  those  between  the  highest  and  lowest  Mammals, 
between  Beaked  Animals  (Orni(hostoma),  Pouched  Animals 
MarsuptaMa),  and  Armadillos  on  the  one  hand,  and  Dogs, 
Apes,  ami  Men  on  the  other.  And  yet  all  those  insects 
belong,  without  question,  to  the  single  class  of  Arthropoda, 
jusi  as  all  these  Mammals  undoubtedly  belong  to  the  single 
class  of  Vertebrates  ;  and  just  as  every  logical  adherent  of 
the  doctrine  of  evolution  must  assume  a  common  parent- 
form  for  all  those  Insects,  so  also  he  must  necessarily  assert 
a  common  descent  for  all  these  Mammals. 


450  THE   EVOLUTION    OF   MAN. 

Turning  now  from  observing  the  comparative  mental 
capacity  of  the  various  animals  to  the  question  as  to  the 
organs  of  these  functions,  we  receive  the  answer,  that  in  all 
higher  animals  they  are  invariably  connected  with  certain 
groups  of  cells,  those  cells  which  compose  the  central 
nervous  system.  All  naturalists,  without  exception,  agree 
that  the  central  nervous  system  is  the  organ  of  the  mental 
life  of  animals,  and  this  assertion  is  at  any  time  capable 
of  experimental  rro>f.  If  the  central  nervous  system  is 
wholly  or  partially  destroyed,  the  "  mind,"  or  the  psychical 
activity  of  the  animal,  is  wholly  or  partially  annihilated  at 
the  same  time.  We  must,  therefore,  next  inquire  what  is 
the  character  of  the  mental  organ  in  man.  The  undeniable 
answer  to  this  question  has  already  been  given.  Man's 
mental  organ  is,  in  its  whole  structure  and  origin,  the  same 
as  that  of  all  other  Vertebrates.  It  originates  as  a  simple 
medullary  tube  from  the  outer  skin  of  the  embryo,  from 
the  skin-sensory  layer,  or  the  first  of  the  secondary  germ- 
layers.  In  the  course  of  its  gradual  development  it  passes 
through  the  same  stages  of  progression  in  the  human 
embryo  as  in  that  of  all  other  Vertebrates,  and  as  these 
latter  have  undoubtedly  a  common  origin,  so  must  also  the 
brain  and  spinal  cord  be  of  the  same  origin  in  all. 

Physiological  observation  and  experiment  teaches,  more- 
over, that  the  relation  of  the  "  mind  "  to  its  organ,  the  brain 
and  spinal  marrow,  is  exactly  the  same  in  Man  as  in  all 
other  Mammals.  The  former  can  in  no  case  act  without 
the  latter;  the  one  is  connected  with  the  other,  as  is 
muscular  movement  with  muscle.  Therefore,  the  mind  can 
develop  only  in  connection  with  its  organ.  Adherents-  of 
the  Theory  of  Descent,  who  concede  the  causal  connection 


DEVELOPMENT   OF  THE  HUMAN    MIND,  45  I 

between  Ontogeny  and  Phylogeny,  arc  now  compelled  to 
recognize  the  following  propositions  :  The  mind,  or  "  psyche," 
of  man  has  developed  together  with,  and  as  the  function  of 
the  medullary  tube,  and  just  as  even  now  the  brain  and 
spinal  marrow  develop  in  each  human  individual  from  the 
simple  medullary  tube,  so  the  human  "  mind,"  or  the  mental 
capacity  of  the  entire  human  race,  has  developed  gradually, 
step  by  step,  from  the  mind  of  lower  A^ertebrates.  Just  as 
even  now  in  every  individual  of  the  human  race  the 
wonderful  and  complex  structure  of  the  brain  develops 
step  by  step  from  exactly  the  same  rudiment,  from  the 
same  five  simple  brain-bladders,  as  in  all  other  Skulled 
Animals  (Graniota),  so  the  human  mind  has  gradually 
developed  in  the  course  of  millions  of  years  from  the  mind 
of  lower  Skulled  Animals ;  and  as  now  the  brain  of  every 
human  embryo  differentiates  according  to  the  special  type 
of  the  Ape-brain,  so  also  the  human  psyche  has  historically 
differentiated  from  the  Ape-mind. 

This  monistic  idea  will,  of  course,  be  indignantly  re- 
jected by  most  people,  who  accept  the  contrary  dualistic 
view,  which  denies  the  inseparable  connection  of  the  brain 
and  the  mind,  and  regards  "  body  and  mind  "  as  entirely 
separate  and  distinct;  but  how  shall  we  reconcile  this 
commonly  accepted  view  with  the  facts  taught  by  the 
history  of  evolution  ?  The  dualistic  view  is,  at  least,  as 
irreconcilably  opposed  to  Ontogeny  as  to  Phylogeny.  If 
we  agree  with  the  majority  of  men,  that  the  mind  is  a  sell- 
existent,  independent  being,  which  has  originally  nothing 
to  do  with  the  body,  but  only  dwells  in  it  for  a  time,  and 
which  gives  expression  to  its  emotions  through  the  brain, 
as  the  piano-player  through  his  instrument,  then  we  must 


452  THE   EVOLUTION   OF   MAN. 

suppose  a  period  in  the  human  germ-history,  at  which  the 
mind  enters  the  body,  enters  the  brain ;  and  we  must  also 
suppose  a  moment  at  death,  at  which  it  leaves  the  body; 
and  further,  as  every  man  inherits  certain  individual 
mental  qualities  from  each  parent,  we  must  suppose  that 
portions  of  the  mind  of  each  were  transferred  to  the  germ 
at  the  time  of  its  procreation.  A  little  piece  of  the  father's 
mind  accompanied  the  sperm-cell,  a  little  piece  of  the 
mother's  mind  remained  with  the  egg-cell.  This  dualistic 
view  entirely  fails  to  explain  the  phenomena  of  evolution. 
We  all  know  that  the  new-born  child  has  no  consciousness, 
no  knowledge  of  itself  and  of  the  objective  world.  Who- 
ever has  children  of  his  own,  and  follows  their  mental 
development  candidly,  cannot  possibly  deny  that  processes 
of  biological  evolution  are  at  work  there.  Just  as  all  other 
functions  of  the  body  develop  in  connection  with  their 
organs,  so  does  the  mind  develop  in  connection  with  the 
brain.  And  this  gradual  development  of  the  child's  mind 
is  such  a  wonderful  and  beautiful  phenomenon,  that  every 
mother  and  every  father  with  eyes  to  see  takes  unwearied 
delight  in  observing  it.  The  text-books  of  Psychology 
alone  are  ignorant  of  any  such  development,  and  we  are 
almost  forced  to  the  conclusion  that  their  authors  them- 
selves never  had  any  children.  The  human  mind,  as  it  is 
represented  in  the  great  majority  of  psychological  works, 
is  only  the  one-sided  mind  of  a  learned  philosopher,  who, 
indeed,  knows  many  books,  but  nothing  of  the  process  of 
evolution,  and  does  not  suspect  that  even  his  own  mind  has 
developed. 

These   same   dualistic  philosophers  must,  of  course,  if 
they  are  consistent,  also  assume  that  there  was  a  moment 


REASON.  453 

in  the  Phylogeny  of  the  human  mind  at  which  this  mind 
first  entered  the  vertebrate  body  of  man.  Accordingly,  at 
the  time  when  the  human  body  developed  from  the  body 
of  the  Anthropoid  Ape  (thus,  probably,  in  the  latter  part  of 
the  Tertiary  Period),  a  specific  human  mind-element — or,  as  it 
is  usually  expressed,  a  "  divine  spark  " — must  have  suddenly 
entered  or  been  breathed  into  the  brain  of  the  Anthropoid 
Ape,  and  there  have  associated  itself  with  the  already 
existing  Ape-mind.  I  need  not  point  out  the  theoretic 
difficulties  involved  in  this  conception.  I  will  only  remark 
that  even  this  "  divine  spark,"  by  which  the  mind  of  Man 
is  said  to  be  distinguished  from  that  of  all  other  animals, 
must  itself  be  a  thing  capable  of  evolution,  and  has  actuall\- 
developed  progressively  in  the  course  of  human  history. 
This  "  divine  spark  "is  usually  understood  to  be  "reason,' 
and  is  ascribed  to  man  as  a  mental  function  distinguishing 
him  from  all  "irrational  animals."  Comparative  Psycho- 
logy, however,  teaches  that  this  frontier-post  between  man 
and  beast  is  altogether  untenable.198  We  must  either  take 
the  idea  of  reason  in  its  broader  sense,  in  which  case  it 
belongs  to  the  higher  Mammals  (the  Ape,  Dog,  Elephant, 
Horse),  as  much  as  to  the  majority  of  men  ;  or  we  must 
conceive  it  in  its  narrower  sense,  and  then  it  is  lacking  in 
the  majority  of  men,  as  well  as  in  most  animals.  On  the 
whole,  that  which  Goethe's  Mephistopheles  said  of  his  time, 
is  true  of  Man's  reason  to-day  : 

"Ho  might  have  kept  himself  more  right 
Hadat  Thou  ne'er  shewn  to  him  a  glimpse  of  heaven's  light. 
He  calls  it  Reason,  but  Thou  seest 
Its  use  but  makes  him  beastlier  than  the  beast." 

If,  therefore,  we  must  abandon  this  generally  preferred, 


454  THE   EVOLUTION   OF   MAN. 

and,  in  many  respects,  very  pleasant  clualistic  theory  of  the 
mind,  as  being  wholly  untenable,  because  irreconcilable 
with  genetic  facts,  then  the  opposite  monistic  view  alone 
remains  to  us.  according  to  which  the  human  mind,  like 
that  of  any  other  animal,  is  a  function  of  the  central  nervous 
system,  with  which  it  has  developed  in  inseparable  con- 
nection. Ontogenetically,  we  see  this  in  every  child ; 
phylogenetically,  we  must  assert  it  in  accordance  with  the 
fundamental  law  of  Biogeny.  In  every  human  embryo 
the  medullary  tube  develops  from  the  skin-sensory  layer, 
and  from  the  anterior  part  of  that  tube  the  five  brain- 
bladders  of  Skulled  Animals  (Graniota),  and  from  these 
the  mammalian  brain  (at  first  with  the  characteristics  of 
the  lower,  then  with  those  of  the  higher  Mammals). 
Just  as  this  entire  ontogenetic  process  is  but  a  short  repro- 
duction, occasioned  by  Heredity,  of  the  same  process  in  the 
Phylogeny  of  Vertebrates,  so  also  the  wonderful  mental 
activity  of  the  human  race  has  gradually  developed,  step 
by  step,  in  the  course  of  many  thousands  of  years,  from  the 
less  perfect  mental  activity  of  the  lower  Vertebrates.  And 
the  evolution  of  the  mind  in  each  child  is  only  a  brief 
reproduction  of  that  long  phylogenetic  process. 

The  extraordinary  and  important  bearing  of  Anthro- 
pogeny  on  Philosophy,  in  the  light  of  the  fundamental  prin- 
ciple of  Biogeny,  now  becomes  apparent.  The  speculative 
philosophers  who  will  take  possession  of  the  facts  of  On- 
togeny and  explain  them  phylogenetically  (according  to  that 
law),  will  introduce  a  greater  advance  in  the  history  of 
Philosophy  than  has  been  made  by  the  greatest  thinkers  of 
all  previous  centuries.  Undoubtedly  every  clear  and  logical 
thinker  must  draw  from  the  facts  of  Comparative  Anatomy 


PHILOSOPHICAL  ASPECT  OF    EVOLUTION.  455 

and  Ontogeny  which  have  been  brought  forward,  a  mass 
of  suggestive  thoughts  and  reflections  which  cannot  fail 
of  their  effect  on  the  further  development  of  the  philo- 
sophical study  of  the  universe.  Neither  can  it  be  doubted 
that  these  facts,  if  properly  weighed,  and  judged  without  pre- 
judice, will  lead  to  the  decisive  victory  of  that  philosophical 
tendency,  which  we  distinguish,  briefly,  as  monistic  or 
mechanical,  in  distinction  from  the  dualistic  or  ideological, 
on  which  most  philosophical  systems  of  ancient,  mediaeval, 
and  modern  times  are  based.  This  mechanical,  or  monistic 
philosophy,  asserts  that  everywhere  the  phenomena  of 
human  life,  as  well  as  those  of  external  nature,  are  under 
the  control  of  fixed  and  unalterable  laws,  that  there  is 
everywhere  a  necessary  causal  connection  between  pheno- 
mena, and  that,  accordingly,  the  whole  knowable  universe 
forms  one  undivided  whole,  a  "  monon."  It  further  asserts, 
that  all  phenomena  are  produced  by  mechanical  causes 
{causae  efficientes),  not  by  pre-arranged,  purposive  causes 
(causa  finales).  Hence  there  is  no  such  thing  as  "free- 
will "  in  the  usual  sense.  On  the  contrary,  in  the  light  of 
this  monistic  conception  of  nature,  even  those  phenomena 
which  we  have  been  accustomed  to  regard  as  most  five  and 
independent,  the  expressions  of  the  human  will,  appear  as 
subject  to  fixed  laws  as  any  other  natural  phenomenon 
Indeed,  each  unprejudiced  and  searching  test  applied  to  the 
action  of  our  "free-will"  shows  that  the  latter  is  never 
really  free,  but  is  always  determined  by  previous  causal 
conditions,  which  are  eventually  referable  either  to  Heredity 
or  to  Adaptation.  Accordingly,  we  cannot  assent  to  the 
popular  distinction  between  nature  and  spirit.  Spirit 
exists  everywhere  in  nature,  and  we  know  of  no  spirit  out- 


456  THE   EVOLUTION   OF   MAN. 

side  of  nature.  Hence,  also,  the  usual  distinction  between 
natural  science  and  mental  science  is  entirely  untenable. 
Every  real  science  is  at  the  same  time  both  a  natural  and  a 
mental  science.     Man  is  not  above  nature,  but  in  nature. 

The  opponents  of  the  doctrine  of  evolution  are  very  fond 
of  branding  the  monistic  philosophy  grounded  upon  it  as 
"materialism,"  by  confusing  philosophical  materialism  with 
the   wholly   different    and    censurable   moral   materialism. 
Strictly,  however,  our  "  monism  "  might,  as  accurately  or  as 
inaccurately,  be  called    spiritualism   as    materialism.     The 
real  materialistic  philosophy  asserts,  that  the  vital  pheno- 
mena of  motion,  like  all  other  phenomena  of  motion,   are 
effects  or  products  of  matter.     The  other,  opposite  extreme, 
spiritualistic    philosophy,    asserts,    on    the    contrary,    that 
matter  is  the  product  of  motive  force,  and  that  all  material 
forms  are  produced  by  free  forces  entirely  independent  of 
the   matter   itself.      Thus,    according   to    the    materialistic 
conception  of  the  universe,  matter,   or  substance,  precedes 
motion,  or  active  force.     According  to  the  spiritualistic  con- 
ception of  the  universe,    on  the  contrary,  active  force  or 
motion  precedes  matter.     Both  views  are  dualistic,  and  we 
hold  them   both   to  be  equally  false.     A  contrast  to  both 
views  is  presented  in  the  monistic  philosophy,  which  can  as 
little  believe  in  force  without  matter,  as  in  matter  without 
force.     It  is  only  necessary  to  reflect  on    this  for  a  time, 
from  a  strictly  scientific  standpoint,  to  find  that  on  close 
examination  it  is  impossible   clearly  to  represent  the  one 
without  the    other.      As  Goethe   says,    "  Matter  can  never 
exist  and  act  without  spirit ;    neither  can   spirit  without 
matter." 12 

The  "  spirit "  and  "  mind  "  of  man  are  but  forces  which 


REASON  A  FUNCTION   OF   MIND.  457 

are  inseparably  connected  with  the  material  substance  of 
our  bodies.  Just  as  the  motive  force  of  our  flesh  is  involved 
in  the  muscular  form-element,  so  is  the  thinking  force  of 
our  spirit  involved  in  the  form-element  of  the  brain.  Our 
spiritual  forces  are  as  much  functions  of  this  part  of  the 
body,  as  every  force  is  a  function  of  a  material  body.  We 
know  of  no  matter  which  does  not  possess  force,  and,  con- 
versely, of  no  forces  that  are  not  connected  with  matter. 
When  the  forces  manifest  themselves  in  the  phenomena  of 
motion,  they  are  called  active  forces;  if,  on  the  other  hand, 
the  forces  are  in  a  state  of  rest,  or  of  equilibrium,  they  are 
called  latent  forces.1"  This  is  as  true  of  inorganic  natural 
substances  as  of  organic.  The  magnet  attracting  iron- 
filings,  powder  exploding,  steam  driving  the  locomotive,  are 
active  inorganic  substances;  they  work  by  active  force  just 
as  does  the  sensitive  mimosa,  when  it  folds  its  leaves  at  a 
touch, — as  does  the  Amphioxus,  when  it  buries  itself  in  the 
sand, — as  does  man,  when  he  thinks.  Only  in  these  latter 
cases  the  combination  of  the  different  forces,  appearing  as 
phenomena  of  motion,  are  much  more  complex  and  much 
Less  easily  recognized  than  in  the  former  cases. 

Anthropogeny  has  led  us  to  the  conclusion  that  even  in 
the  entire  history  of  the  evolution  of  man,  in  the  history  of 
the  germ,  as  well  as  in  that  of  the  tribe,  no  other  active 
forces  have  been  at  work,  than  in  the  rest  of  organic  and 
inorganic  nature.  All  the  forces  at  work  there  can  be 
reduced  at  last  to  growth — to  that  fundamental  function  of 
evolution  by  which  the  forms  of  inorganic,  as  well  as  of 
organic  bodies,  originate.  Growth,  again,  itself  rests  on  the 
attraction  and  repulsion  of  lil<«-  and  unlike  particles.194  It 
has  given  rise  to  Man  and  to  Ape,  to  Palm  and  Alga,  to 


458  THE    EVOLUTION   OF   MAN. 

crystal  and  water.  Hence  the  evolution  of  man  has  taken 
place  according  to  the  same  "  eternal,  immutable  laws," 
as  has  the  evolution  of  any  other  natural  body. 

It  is  true  that  the  prejudices  that  stand  in  the  way  of 
the  general  recognition  of  this  "  Natural  Anthropogeny ': 
are  even  yet  intensely  powerful ;  otherwise  the  ancient 
strife  between  the  various  philosophical  systems  would 
already  have  been  decided  in  favour  of  "  Monism."  But 
it  can  be  foreseen  with  certainty  that  a  more  general 
acquaintance  with  genetic  facts,  will  gradually  destroy 
those  prejudices  and  bring  about  the  victory  of  the 
natural  idea  of  "Man's  Place  in  Nature."  The  fear  is 
often  expressed  in  opposition  to  this  view  that  it  will  cause 
a  retrogression  in  the  intellectual  and  moral  development 
of  man ;  but,  on  the  contrary,  I  cannot  withhold  my  convic- 
tion, that  the  very  reverse  will  be  true,  that  by  it  the  pro- 
gressive development  of  the  human  spirit  will  be  advanced 
in  an  unusual  degree.  At  all  events,  I  hope  and  trust  that 
I  have,  in  these  chapters,  afforded  convincing  proof  that 
the  only  way  to  attain  a  true  scientific  knowledge  of  the 
human  organism,  is  by  employing  the  method  which  we 
must  acknowledge  to  bo  alone  correct  and  successful  in  the 
study  of  organic  nature, — by  following  the  course  of  the 
History  of  Evolution.200 


NOTES. 

REMARKS  AND  REFERENCES  TO  LITERATURE. 


1  (vol.  i.  p.  2).  Antliropogeny  (Greek)  =  History  of  the  Evolu- 
tion of  Man;  from  Anthropos  (avOpwiros)  =  man,  and  genea  (yeved) 
=  Evolution  history.  There  is  no  especial  Greek  word  for  "the 
history  of  evolution;"  in  its  place  is  used  either  yevea  (=  de- 
scent), or  yoviia.  (=  generation).  If  goneia  is  preferred  to 
genea,  the  word  must  be  written  Anthropogony.  The  word 
"  Anthroporiony"  used  first  by  Josephus,  means,  however,  only 
"  the  generation  of  man."  Genesis  (yeVecrts)  means  "  origination, 
or  evolution  ;  "  therefore  Anthr  ovogenesis  =  "  the  evolution  of 
man." 

2  (i.  3).  Embryo  (Greek)  =  germ  (Z/j.(3pvov).  Really  to  cVtos 
tt/s  yao-T-pos  fipvov  (Eust.),  i.e.  the  unborn  germ  in  the  mother's 
body  (Latin  foetus,  or,  better,  fetus).  In  accordance  with  this 
original  sense,  the  term  embryo  should  only  be  applied  to  those 
young  organisms  which  are  still  enclosed  in  the  egg-coverings. 
(Cf.  "  Generelle  Morphologie,"  vol.  ii.  p.  20.)  Inaccurately,  how- 
ever, various  free-moving  young  forms  of  low  animals  (larva?) 
are  often  spoken  of  as  embryos.     Embryonic  life  ends  at  birth. 

3  (i.  5).  Embryology  (Greek)  =  Germ-science,  from  embrvon 
(Ipfipvov)  =  germ,  and  logos  (Ao'yos)  =  science.  Even  now  the 
whole  history  of  the  evolution  of  the  individual  is  erroneously 
called  "embryology."  For  corresponding  with  the  term 
"embryo"  (see  note  2),  by  "embryology,"  or  "  cmbryogony," 
should  only  be  understood  "  the  history  of  the  evolution   of  the 


460  NOTES. 

individual  within  the  egg-coverings."  As  soon  as  the  organism 
has  left  there,  it  is  no  longer  a  real  "  embryo."  The  later  changes 
of  this  form  the  subject  of  the  science  of  Metamorphoses,  or 
Metamorph  0  logy. 

4  (i.  5).  Ontogeny  (Greek)  =  "germ-history,"  or  "the 
history  of  the  evolution  of  the  individual;"  from  6vra  =  indi- 
viduals, and  genea  (yevea)  =  history  of  evolution.  (Cf.  note  1.) 
Ontogeny,  as  the  "history  of  the  evolution  of  the  individual," 
embraces  both  Embryology  and  Metamorphology  (note  3). — 
"  Generelle  Morphologie,"  vol.  ii.  p.  30. 

5  (i.  5).  Phytogeny  (Greek)  =  tribal  history,  or  "  the  pa- 
loeontological  history  of  evolution  ;  "  from  phylon  (<£uAov)  =  tribe, 
and  genea  (yevea)  =  history  of  evolution.  The  phylon  includes 
all  organisms  connected  by  blood,  which  are  descended  from  a 
common  typical  parent-form.  Phylogeny  includes  Palaeontology 
and  Genealogy. — "  Generelle  Morphologie,"  vol.  ii.  p.  305. 

6  (i.  6).  Biogeny  (Greek)  =  the  history  of  the  evolution  of 
organisms  or  of  living  natural  bodies  in  the  widest  sense. 
(Genea  tu  biu.)     y3i'os  =  life. 

7  (i.  6).  The  fundamental  law  of  Biogeny.  Cf.  my  "General 
History  of  the  Evolution  of  Organisms"  ("  Generelle  Morphologie," 
1866,  vol.  ii.),  p.  300  (Essays  on  the  causal  connection  of  biogenetic 
and  phyletic  evolution)  ;  also  the  "  Monograph  of  Chalk 
Sponges  "  ("  Monographic  der  Kalkschwiimme,"  1872,  vol.  i.  471); 
also  my  "  Natural  History  of  Creation." 

8  (i.  10).  Palingenesis  (Greek)  =  original  evolution,  from 
palingenesia  (7raAivyei/eo-ia)  =  new-birth,  renewal  of  the  former 
course  of  evolution.  Therefore,  Palingeny  =  inherited  history 
(from  iraktv  =  reproduced,  and  yevea=history  of  evolution). 

9  (i.  10).  Kenogenesis  (Greek)  =  modified  evolution,  from 
kenos  (k£vos)  =  strange,  meaningless;  and  genea  (yevea)  =  history 
of  evolution.  The  modifications  introduced  into  Palingenesis 
by  Kenogenesis  are  vitiations,  strange,  meaningless  additions  to 
the  original,  true  course  of  evolution.  Kenogeny  =  vitiated 
history. 

10  (i.    12).    Latin   definition   of    the   fundamental    law    of 


NOTES.  461 

Biogeny  :  "  Ontogenesis  summarium  vel  rccapitulatio  est  phy- 
logencseos,  tanto  integrius,  quanto  hereditate  palingenesis  con- 
servatm*,  tanto  minus  integrum,  quanto  adaptatione  kenogenesis 
introducitup."  Cf.  my  "Aims  and  Methods  of  Recent  History 
of  Evolution  "  ("  Ziele  und  Wege  der  Heutigen  Entwickelungs- 
geschichte,"  p.  77.     Jena,  1876). 

11  (i.  17).  Mechanical  and  purposive  causes.  Mechanical 
natural  philosophy  assumes  that  throughout  nature,  in  organic 
as  well  as  in  inorganic  processes,  only  non-purposive,  mechanical, 
necessarily-working  caiiscs  exist  (causce  efficientes,  mechanism, 
causality).  On  the  other  hand,  vitalistic  natural  philosophy 
asserts  that  the  latter  are  at  work  only  in  inorganic  processes, 
which  in  certain  other,  purposive,  special  causes  are  at  work, 
conscious  or  purposive  causes,  working  for  a  definite  end  {causa; 
finales,  Vitalism,  Teleology).  (Cf.  "  Generelle  Morphologie," 
vol.  i.  p.  94.) 

12  (i.  17).  Monism  and  Dualism.  Unitary  philosophy,  or 
Monism,  is  neither  extremely  materialistic  nor  extremely  spirit- 
ualistic, hut  resembles  rather  a  union  and  combination  of  these 
opposed  pi-inciples,  in  that  it  conceives  all  nature  as  one  whole 
and  nowhere  recognizes  any  but  mechanical  causes.  Binary 
philosophy,  on  the  other  hand,  or  Dualism,  regards  nature  and 
spirit,  matter  and  force,  inorganic  and  organic  nature  as  distinct 
and  independent  existences.     (Cf.  vol.  ii.  p.  456.) 

13  (i.  20).  Morphology  and  Physiology.  Morphology  (as 
the  science  of  forms)  and  Physiology  (as  the  science  of  the 
functions  of  organisms)  are  indeed  connected,  but  co-ordinate 
sciences,  independent  of  each  other.  The  two  together  constitute 
Biology,  or  the  "  science  of  organisms."  Each  has  its  peculiar 
methods  and  aids.  (Cf.  "  Generelle  Morphologie,"  vol.  i.  pp. 
17-21.) 

11  (i.  21).  Morphogeny  and  Physiogeny.  Biogeny,  or  the 
"  history  of  the  evolution  of  organisms,"  up  to  the  present  time 
has  been  almost  exclusively  Morphogeny.  Just  as  this  first 
opens  the  way  to  a  true  knowledge  of  organic  forms,  so  will 
Physiogeny  afterwards    make   a  true   recognition   of    functions 


462  NOTES. 

possible,  by  discovering  their  historic  evolution.  Its  future 
promises  to  be  most  fruitful.  Cf.  "  Aims  and  Methods  of  the 
Recent  History  of  Evolution"  ("  Ziele  und  Wege  der  Heutigen 
Entwickelungsgcsckichte,"  pp.  92-98.     Jena,  1876). 

15  (i.  27).  Aristotle.  Five  books  on  the  generation  and 
evolution  of  animals  (7repi  £o)tov  yeveVeos). 

16  (i.  28).  Parthenogenesis.  On  "  virginal  generation," 
or  the  "immaculate  conception"  of  Invertebrates,  especially  of 
Articulated  Animals  (Crustacea,  Insecta,  etc.),  see  Siebold, 
"Remarks  on  Parthenogenesis  among  Arthropoda  "  ("  Beitnige 
zur  Parthenogenesis  der  Arthropoden."  Leipzig,  1871).  Georg 
Seidlitz,  "  Parthenogenesis  and  its  Relation  to  other  Forms  of 
Generation  in  the  Animal  Kingdom  "  ("  Die  Parthenogenesis  und 
ibr  Verhaltniss  zu.  den  iibrigen  Zeugungs-Arten  im  Thierreich." 
Leipzig,  1872). 

17  (i.  84).  The  Prefonnation-theory.  This  theory  is,  in 
Germany,  usually  called  "  Evolutions-theorie,"  in  distinction  from 
the  "  Epigenesis-theorie."  As,  however,  in  England,  France,  and 
Italy,  the  latter  is,  on  the  contrary,  usually  called  the  theory  of 
evolution,  evolution  and  epigenesis  being  used  as  synonymous 
terms,  it  appears  better  to  call  the  former  "the  theory  of  pre- 
formation." Recently  Kolliker  has  called  his  "theory  of  hetero- 
genous   generation"  "Evolutionism"  (note    47).     Cf.  preface, 

p.  XXX. 

18  (i.  37).  Alfred  Kirchhoff,  "Caspar  Friedrich  Wolff,  his 
Life  and  Teaching  in  the  Science  of  Organic  Evolution." — 
"  Jenaische  Zeitsekrift  fiir  Naturwissenschaft,"  18G8,  vol.  iv. 
p.  193. 

19  (i.  43).  Part  of  the  writings  left  by  Wolff  have  not  yet 
been  published.  His  most  important  works  are  the  dissertation 
for  the  degree  of  doctor,  Theoria  generationis  (1759),  and  his 
model  treatise  "  de  formatione  intestinorum  "  (on  the  formation 
of  the  intestinal  canal). — "Nov.  Comment.  Acad.  Sc.  Petropol.," 
xii.  1768;  xiii.  1769.  Translated  into  German  by  Meckel. 
Halle,  1812. 

20  (i.  51).  Christian  Pander,  "His toria  metamcnylwseos,  quam 


NOTES.  463 

ovum  incubatum  prioribus  quinque  diebus  subit."  Vicebergi, 
1817.  (Dissertatio  inauguralis.)  "Contributions  toward  tbe 
history  of  the  evolution  of  the  chick  within  the  egg."  ("  Beitrage 
zur  Entwickelungsgeschichte  des  Hiihnchens  im  Eie."  Wttrz- 
burg,  1817.) 

21  (i.  52).  Karl  Ernst  Baer,  "  On  the  Evolution  of  Animals. 
Observations  and  Reflections"  ("  Ueber  Entwickelungsgeschichte 
der  Thiere.  Beobachtung  und  Reflexion."  2  vols.  Konigsberg, 
1827-1837).  In  addition  to  this  chief  work,  cf.  "  Story  of  the 
Life  and  Writings  of  Dr.  Karl  Ernst  Baer,  told  by  himself " 
("  Nachrichten  iiber  Leben  und  Schriften  des  Dr.  Karl  Ernst 
Baer,  mitgetheilt  von  ihm  selbst."     Petersburg,  1865). 

22  (i.  GO).  Albert  Kolliker.  His  "History  of  the  Evolution  of 
Man  and  the  Higher  Animals"  ("  Entwickelungsgeschichte  des 
Menscken  und  der  hoheren  Thiere").  The  2nd  (corrected)  edition, 
1876,  contains  (pp.  28-40)  a  catalogue  of  ontogenetic  literature. 
On  the  newer  contributions  to  this,  cf.  the  "  Jahresberichte 
fiber  die  Leistungen  und  Fortschritte  der  Medicin  "  (Berlin),  by 
Virchow  and  Hirsch  (the  "  History  of  Evolution,"  by  Waldeyer) ; 
also  the  "  Jahresberichte  iiber  die  Fortschritte  der  Anatomie  und 
Physiologie,"  by  Hofmann  and  Schwalbe  (Leipzig)  ;  the  "History 
of  Evolution,"  by  R.  Hertwig  and  Nitsche.  Most  of  Kowalev- 
sky's  researches  are  contained  in  the  "  Memoires  de  l'Academie 
imperiale  de  St.  Petersburg  "  (from  the  year  1866).  Others  are 
published  in  Max  Schultze's  "Archiv  fur  mikroskopische 
Anatomie,"  and  in  other  periodicals. 

23  (i.  60).  Theodor  Schwann,  "Microscopic  Researches  into 
the  Identity  in  Structure  and  Growth  of  Plants  and  Animals  " 
("  Mikroskopische  Untersuchungen  iiber  die  Uebereinstimmung 
in  der  Structur  und  Wachsthum  der  Thiere  und  Pflanzen." 
Berlin,  1839). 

24  (i.  60).  Ernst  Haeckel,  the  Gastrrea  Theory,  phylogenetic 
classification  of  the  animal  kingdom  and  homology  of  the  germ- 
lavers. — "  Jenaische  Zeitschrift  fur  Naturwissenschaft,"  vol.  viii. 
1874,  pp.  1-56. 

25  (i.    75).    Ernst    Haeckel,    "  The    History   of   Creation." 

London,  1876. 

43 


464  NOTES. 

26  (i.  81).  Fritz  Schultze,  "Kant  and  Darwin."  A  con- 
tribution to  the  history  of  the  science  of  evolution.     Jena,  1875. 

27  (i.  81).  Immanuel  Kant,  "Critique  of  Teleological  Rea- 
son" ("Kritik  der  teleologischen  Urtheilskraft  ").  1790.  §  74 
and  §  79.     Cf.  also  my  "  History  of  Creation,"  vol.  i.  p.  103. 

28  (i.  83).  Jean  Lamarck,  "  Philosophie  Zoologique,  ou 
Exposition  des  Considerations  relatives  a  l'histoire  naturelle  des 
animaux,"  etc.  2  Tomes.  Paris,  1809.  Nouvelle  edition,  revue 
et  precedee  d'une  introduction  biographique  par  Charles  Martins. 
Paris,  1873. 

29  (i.  88).  Wolfgang  Goethe  on  Morphology  (zur  Morpho- 
logic). The  formation  and  re-formation  of  organic  bodies.  On 
Goethe's  morphological  studies,  cf.  Oscar  Schmidt  ("  Goethe's 
Verhaltniss  zu  den  organischen  Naturwissenschaften."  Jena, 
1853).  Rudolph  Virchow,  "Goethe  as  a  Naturalist"  (Berlin, 
1861).  Helmholtz,  "On  Goethe's  Natural  Scientific  Works" 
(Brunswick,  1865). 

30  (i.  96).  Charles  Darwin.  His  chief  work  is  "  On  the 
Origin  of  Species  by  means  of  Natural  Selection  "  (1859). 

31  (i.  99).  Darwin  and  Wallace.  The  general  outlines  of 
the  theory  of  selection  were  discovered  independently  by  Darwin 
and  Wallace.  It  does  not,  however,  follow  that  the  services 
of  the  latter  in  furthering  the  science  of  evolution  are  at  all 
comparable  with  those  of  the  former.  As  many  opponents  of 
Darwin,  especially  the  English  Jesuit  Mivart,  have  recently 
endeavoured  to  exalt  Wallace  at  the  expense  of  Darwin,  and  to 
depreciate  the  latter,  I  take  this  opportunity  of  expressly  assert- 
ing that  Darwin's  services  are  very  far  the  greater. 

32  (i.  101).  Thomas  Huxley.  In  addition  to  the  works 
mentioned  in  the  text,  the  following  popular  works  are  especially 
to  be  recommended  :  "  On  Our  Knowledge  of  the  Causes  of 
Phenomena  in  Organic  Nature,"  and  the  "  Elementary  Phy- 
siology" (1871). 

33  (i.  101).  Gustav  Jaeger,  "  Zoological  Letters"  ("Zoologische 
Briefe."  Vienna,  1876),  and  the  "  Text-book  of  General  Zoology" 
("  Lehrbuch  der  Allgemeinen  Zoologie."     Stuttgart,  1875). 


NOTES.  465 

34  (i.  101).  Friedrich  Rolle,  "Man,  his  Descent  and  Morality 
represented  in  the  light  of  the  Darwinian  Theory,  and  on  the 
basis  of  Recent  Geological  Discoveries"  ("  Der  Mensch,  seine 
Abstammung  and  Gesittung  im  Lichte  der  Darwin'schen  Lchre," 
etc.).     Frankfort,  1866. 

35  (i.  102).  Ernst  Haeckel,  "  Generelle  Morphologie  der 
Organisinen."  General  outlines  of  the  science  of  organic  forms, 
mechanically  shown  in  accordance  with  the  theory  of  descent  as 
reformed  by  Charles  Darwin.  Vol.  i ,  "  General  Anatomy  ;  " 
vol.  ii.,  "  General  History  of  Evolution. "     Berlin,  1866. 

36  (i.  103).  Charles  Darwin,  "The  Descent  of  Man,  and 
Selection  in  Relation  to  Sex."     2  vols.     London,  1871. 

37  (i.  108).  Karl  Gegenbaur,  "Outlines  of  Comparative 
Anatomy"  ("  Grundziige  der  vergleichenden  Anatomic"  Leipzig. 
2nd  ed.,  1870).  "Elements  of  Comparative  Anatomy  "  ("  Grundriss 
der  vergleichenden  Anatomie."     3rd  (improved)  edition,  1874). 

38  (i-  114).  Migration-theory.  Moritz  Wagner,  "  The  Dar- 
winian Theory  and  the  Law  of  Migration  of  Organisms  "  ("  Die 
Darwin'sche  Theorie  und  das  Migrations-gesetz  der  Organ- 
ismen."  Leipzig,  1868).  August  Weismann,  "  On  the  Influence 
of  Isolation  in  the  Formation  of  Species  "  ("  Ueber  den  Einfluss 
der  Isolirung  auf  die  Artenbidung."     Leipzig,  1871). 

39  (i.  116).  Carus  Sterne,  "Evolution  and  Dissolution"  ("Wer- 
den  und  Vergehen ").  A  popular  history  of  the  evolution  of 
nature  as  a  whole.  Berlin,  1876.  Agassiz  a  "founder"  of 
natural  science.     "  Gegenwart."     Berlin,  1876. 

40  (i.  117).  Ernst  Haeckel,  "The  Chalk-sponges"  ("Die 
Kalkschwainme ;  Calcispongien  oder  Grantien."  Berlin,  1872). 
A  monograph  and  an  attempted  solution  of  the  problem  of  the 
origin  of  species.  Vol.  i.,  "  Biology  of  Chalk-sponges  ;  "  vol.  ii., 
"Classification  of  Chalk-sponges;"  vol.  iii.,  "Atlas  of  Chalk- 
sponges  "  (with  60  plates). 

41  (i.  124).  On  the  Individuality  of  Cells  and  recent  reforms 
in  the  cell-theory,  of.  my  "  individualitiitslehre,"  or  "  Tectologie  " 
(•'Generelle  Morphologie,"  vol.  i.  pp.  239-274).  Rudolf 
Virchow,  "  Collular  Pathologie."     4th  edition.     Berlin,  1871. 


466  NOTES. 

42  (i.  130).  "The  Plastid-theory  and  the  Cell-theory."— 
"  Jenaische  Zeitschrift  fur  Naturwissenschaft,"  1870,  vol.  v.  p. 
492. 

43  (i.  138).  Gegenbaur,  "  On  the  Structure  and  Evolution  of 
Vertebrate  Eggs  with  Partial  Yelk-cleavage." — "  Archiv  f.  Anat. 
u.  Phys."  1861,  p.  491. 

44  (i.  153).  Ernst  Haeckel,  "On  Division  of  Labour  in  Nature 
and  Human  Life,"  in  the  collection  of  Lectures  by  Virchow- 
Holtzendorf,  1 869.     Sect.  78      2nd  edition. 

45  (i.  160).  Monogony  {Generatio  neutralis).  On  the  various 
forms  of  asexual  reproduction  (Schizogony,  Sporogony,  etc.),  cf. 
"  Generelle  Morphologie,"  vol.  ii.  pp.  36-58. 

46  (i.  160).  Amphigony  (Generatio  sexualis).  On  the  various 
forms  of  sexual  reproduction  (Hermaphroditism,  Gonochorism, 
etc.),  see  "  Generelle  Morphologie,"  vol.  ii.  pp.  58-69. 

47  (i.  168).  Fitful  evolution  and  gradual  evolution.  The 
theory  of  fitful  evolution  has  recently  been  developed  especially 
by  Kolliker,  who,  under  the  title  of  heterogeneous  generation, 
opposes  it  to  gradual  evolution  as  maintained  by  us  ("  Zeitschr. 
f.  Wissens.  Zool.,"  vol.  xiv.  1864,  p.  181,  and  "  Alcyonaria,"  1872, 
pp.  384-415).  This  theory  is  distinguished  by  assuming  entirely 
unknown  causes  for  the  "fitful  evolution  of  species,"  a  so-called 
"  great  law  of  evolution  "  (an  empty  word  indeed  !).  On  the 
contrary,  we  see,  with  Darwin,  in  the  facts  of  Heredity  and 
Adaptation  sufficient  known  (partly  inner,  partly  external) 
physiological  causes,  which  explain  the  gradual  evolution  of 
species  under  the  influence  of  the  struggle  for  existence. 

48  (i.  170).  Immaculate  Conception  never  occurs  in  the 
vertebrate  tribe.  On  the  other  hand,  parthenogenesis  frecpaently 
occurs  among  Articulated  Animals  (Arthropoda)  (note  16). 

49  (i.  171).  Fertilization  of  Flowers  by  insects.  Charles 
Darwin  on  "  The  various  contrivances  by  which  British  and 
Foreign  Orchids  are  fertilized  by  Insects."  Hermann  Midler  on 
"  The  Fertilization  of  Flowers  by  Insects,  and  the  correlative 
adaptations  of  both  "  ("  Die  Befruchtung  der  Blumen  durch 
Insecten  und  die  gegenseitigen  Anpassungen  Beider  ") .     A  con- 


NOTES.  467 

tribution   to   our  knowledge   of    causal   connection   in   organic 
nature.     Leipzig,  1873. 

50  (i.  178).  The  Process  of  Fertilization  has  been  very 
variously  viewed,  and  was  formerly  often  regarded  as  an 
entirely  mysterious  process,  or  even  as  a  supernatural  miracle. 
It  now  appears  no  more  "  wonderful  or  supernatural  "  than  the 
process  of  digestion,  of  muscular  movement,  or  of  any  other 
physiological  function.  For  the  earlier  views,  cf.  Leuckart, 
Article  "  Zeugung  "  (generation)  in  R.  Wagner's  "  Dictionary 
of  Physiology,"  1850. 

51  (i.  179).  Monerula.  The  simple,  very  transient,  kernel- 
less  condition,  which  we  briefly  call  the  "monerula,"  and,  in 
accordance  with  the  fundamental  law  of  Biogeny,  regard  as  a 
palingenetic  reproduction  of  the  phylogenetic  Moneron  parent- 
form,  appears  to  vary  to  some  extent  in  different  organisms, 
especially  in  the  matter  of  duration.  In  those  cases  in  which 
it  no  longer  occurs,  and  in  which  the  kernel  of  the  fertilized 
egg  persists  wholly  or  partially,  we  may  regard  this  phenomenon 
as  a  later,  kenogenetic  curtailment  of  Ontogeny. 

52  (i.  181).  The  Plasson  of  the  monerula  appears,  mor- 
phologically, a  homogeneous  and  structureless  substance,  like 
that  of  the  Moneron.  This  is  not  contradicted  by  the  fact  that 
we  ascribe  a  very  complex  molecular  structure  to  the  plastidules, 
or  "  plasson-molecules,"  of  the  monerula ;  this  latter  will 
naturally  be  more  complex  in  proportion  as  the  organism  which 
it  ontogenetically  constitutes  is  higher,  and  as  the  ancestral 
scries  of  that  organism  is  longer,  in  proportion  as  the  preceding 
processes  of  Heredity  and  Adaptation  are  more  numerous. 

53  (i.  182).  The  Fundamental  Significance  of  the  Parent-cell, 
or  cytula,  as  the  foundation-stone  of  the  young  organism  in  the 
course  of  development,  can  only  be  rightly  appreciated,  if  the 
part  taken  in  its  constitution  by  the  two  generating  cells  is 
rightly  appreciated,  the  part  taken  by  the  male  sperm-cell  and 
by  the  female  fgg-cell. 

54  (i.  183).  The  One-celled  Germ-organism,  like  the  act  of 
fertilization   from    which   it    results,    has    been   very    variously 


468  NOTES. 

viewed.  Cf.  on  this  subject,  in  addition  to  the  four  important 
works,  here  quoted,  by  Auerbach,  Biitschli,  Hertwig,  and  Stras- 
burger,  the  most  recent  annals  of  the  progress  of  the  history  of 
evolution  (Waldeyer  in  Virchow-Hirsch's  "  Jab.resbericb.ten," 
Berlin ;  Hertwig  in  Hof  mann-Schwalbe's  "  Jahresbei'ichten," 
Leipzig). 

55  (i.  185).  Protozoa  and  Metazoa.  Cf.  vol.  i.  p.  248;  ii.  92. 
The  Protozoa  and  Metazoa  are  genetically  and  anatomically  so 
very  distinct,  that  the  former,  as  Protista,  may  even  be  excluded 
entirely  from  the  animal  kingdom,  and  may  be  regarded  as  a 
neutral  intermediate  kingdom  between  the  plant  and  animal 
kingdoms. — "  Generelle  Morphologic,"  vol.  i.  pp.  191-230.  Ac- 
cording to  this  view  the  Metazoa  alone  are  really  animals. 

56  (i.  186).  The  Unity  of  the  Zoogenetic  Conception,  result- 
ing from  the  Gastra?a-theory,  has  as  yet  not  been  destroyed  bv 
the  numerous  attacks  directed  against  that  theory :  for  none  of 
these  attacks  have  succeeded  in  substituting  anything  positive ; 
by  pure  negation  no  advance  can  be  made  in  this  dark  and 
difficult  subject. 

57  (i.  187).  The  Egg-cleavage  and  Gastrulation  of  Man,  as 
represented  diagrammatically  in  Figs.  12-17  of  Plate  II.,  is  most 
probably  in  no  essential  way  different  from  that  of  the  Rabbit, 
which  has  as  yet  been  most  closely  examined  in  this  point. 

58  (i.  188).  Ernst  Haeckel,  "  Arabian  Corals  "("  Arabische 
Korallen").  "A  Journey  to  the  Coral  Banks  of  the  Red  Sea,  and 
a  Glimpse  into  the  Life  of  Coral  Animals.  A  popular  lecture, 
with  scientific  explanations."  With  5  coloured  plates,  and  20 
woodcuts.     Berlin,  1876. 

59  (i.  189).  The  Number  of  the  Segmentella,  or  cleavage- 
cells,  increases,  in  the  original,  pure  forms  of  palingenetic  egg- 
cleavage,  in  regular  geometric  progression.  But  the  point  to 
which  this  proceeds  varies  in  the  various  archiblastic  animals, 
so  that  the  Morula,  as  the  final  result  of  the  cleavage-pi'ocess, 
consists  sometimes  of  32,  sometimes  of  64,  sometimes  of  128 
cells,  and  so  on. 

60  (i.  189).    The   Mulberry-germ,    or   Morula.      The   seg- 


NOTES.  469 

montclla,  or  cleavage-cells,  which  constitute  the  Morula  at  the 
close  of  palingenetic  egg-cleavage,  generally  appear  entirely 
similar,  with  morphological  difference  in  size,  form,  or  con- 
stitution. This  does  not,  however,  hinder  the  fact  that  these 
cells  have  separated,  even  during  cleavage,  into  animal  and 
vegetable  cells,  have  differentiated  physiologically,  as  is  indicated 
in  Figs.  2  and  3,  Plate  II.,  as  probable. 

61  (i.  189).  The  Bladder-germ  of  Archiblastic  Animals 
{blastula,  or  blastosjjhcera),  which  is  now  commonly  known  as 
the  germ- vesicle,  or,  more  accurately,  as  the  "  germ-membrane 
vesicle,"  must  not  be  confused  with  the  essentially  different 
11  germ-vesicle  "  of  amphiblastio  mammals,  which  is  better  called 
the  "intestinal-germ  vesicle"  (gastrocystis).  The  gastrocystis 
and  the  blastula  are  still  often  united  under  the  name  of  "  germ- 
vesicle,  or  vesicula  blastodermica."     Cf.  vol.  i.  p.  290. 

62  (i.  .192).  The  Definition  of  the  Gastrula  was  first 
established  by  me  in  1872,  in  my  "Monograph  of  Chalk-sponges  " 
(vol.  i.  pp.  333,  34:5,  466).  There  I  already  gave  due  weight  to 
the  "  extremely  great  significance  of  the  gastrula  in  reference 
to  the  general  Phylogeny  of  the  animal  kingdom"  (p.  333). 
"  The  fact  that  these  larval  forms  re-occur  in  the  most  different 
animals,  cannot,  I  think,  be  sufficiently  estimated,  and  bears 
plain  witness  to  the  former  common  descent  of  all  from  the 
Gastrcea  "  (p.  345). 

63  (i.  194).  The  Uniaxial  Outline  of  the  Gastrula  is,  on 
account  of  the  two  different  poles  of  the  axis,  more  accurately, 
described  as  a  diplopolic  uniaxial  form  (a  sternometric  outline  : 
eonoid-form,  or  cone).  Cf.  my  "  Promorphology  "  ("  Generelle 
Morphologic,"  vol.  i.  p.  426). 

64  (i.  194).  Primitive  Intestine  and  Primitive  Month.  M\ 
distinction  of  the  primitive  intestine  and  primitive  mouth 
(protogaster  and  protostoma)  from  the  later,  permanent  intestine 
and  mouth  (metagastcr  and  metastoma)  has  been  variously 
attacked;  it  is,  however,  as  much  justified  as  the  distinction  of 
the  primitive  kidney  from  the  permanent  kidney,  of  the  primitive 
vertebrae  from  the  permanent  vertebra?.     The  primitive  intestine 


470  NOTES. 

forms  but  a  part  of  the  permanent  intestine,  and  the  primitive 
mouth  (at  least  in  the  higher  animals)  does  not  become  the 
permanent  mouth. 

G5  (i.  196).  Primitive  germ-layers  (blastophylla) .  As  the 
two  primary  germ-layers  (entoderma  and  exoderma)  originally 
form  the  sole  histogenetic  rudiment  of  the  whole  body,  and  as 
the  mesoderma,  the  nutritive  yelk,  and  all  other  accessory  parts 
of  the  germ  have  developed  only  secondarily  from  the  former, 
1  consider  it  very  important  to  distinguish  between  the  primary 
and  secondary  germ-layers.  The  latter,  to  distinguish  them 
from  the  former,  might  be  called  "  after  germ-layers "  (blas- 
telasma) . 

66  (i.  201).  Unequal  Cleavage  and  Hood-gastrula  (Sec/- 
mentatio  incequalis  et  Amjrfdgastrida).  Next  to  Amphibia  the 
most  accessible  examples  for  observation  of  unequal  cleavage 
and  the  Amphigastrula  are  afforded  by  the  indigenous  Soft- 
bodied  Animals  (Mollusca)  and  Worms  (Snails  and  Mussels, 
Earth  Worms  and  Leeches). 

67  (i.  202).  The  Colour  of  Amphibian-eggs  is  occasioned  by 
the  accumulation  of  dark  colouring-matter  at  the  animal  pole  of 
the  egg.  In  consequence  of  this  the  animal-cells  of  the  exoderm 
appear  darker  than  the  vegetative  cells  of  the  entoderm.  In 
most  animals  the  reverse  is  the  case;  the  protoplasm  of  the 
entoderm  cells  being  usually  darker  and  more  coarsely  granulated 
(vol.  i.  p.  197). 

68  (i.  207).  Hood-gastrula  of  Amphibia.  Cf.  Robert  Remak, 
"  On  the  Evolution  of  Batrachia  "  ("  Ueber  die  Entwickelung  der 
Batrachier,"  p.  126  ;  Plate  XII.  Figs.  3-7).  Strieker's  "  Manual 
of  Tissues"  ("Handbuch  der  Gewebelehre,"  vol.  ii.  p. 1195- 
1202 ;  Figs.  399-402).  Goette,  "  History  of  the  Evolution  of 
Bombinator"  ("  Entwickelungsgeschichte  der  Unke,"  p.  145; 
Plate  II.  Figs.  32-35). 

69  (i.  214).  Hood-gastrula  of  Mammals.  Eduard  van 
Beneden,  "  La  maturation  de  l'ceuf,  la  fecondation  et  les  premieres 
phases  du  developpement  embryonnaire  des  Mammiferes,  d'apres 
des  recherches  faites  chez  le  lapin."     Brussels,  1875.     No  figures 


NOTES.  47I 

are  given  with  these  "  Communication  preliminaire ; "  Van 
Beneden's  description  is,  however,  so  clear,  so  thorough  and  care- 
ful, that  they  afford  an  entirely  satisfactory  insight  into  unequal 
egg-cleavage  and  the  formation  of  the  Hood-gastrula  in  Mammals. 
All  other  observers,  who  have  studied  the  germination  of  Mam- 
malian eggs  (among  the  most  recent  Kolliker,  Rauber,  and 
Hewson  may  be  especially  mentioned),  have  overlooked  or 
failed  to  recognize  the  important  features  discovered  by  Van 
Beneden. 

70  (i.  218).  The  Disc-gastrula  (Disco-gastrula)  of  Osseous 
Fishes  (Teleostei).  Van  Bambeke,  "  Recherches  sur  l'embry- 
ologie  des  poissons  osseux."  Brussels,  1875.  The  transparent 
Fish-eggs,  in  which  I  observed  discoid  cleavage  (Scgmentatio 
discoidalis)  and  the  formation  of  the  Disc-gastrula  by  invagination, 
are  accurately  described  in  my  article  on  "  The  Gastrula  and 
Egg-cleavage  of  Animals  "  ("  Jen.  Zeitschrift  fur  Naturwis- 
senschaft,"  1875,  vol.  ix.  p.  432-444;  PJates  IV,  V).  On  the 
Disc-gastrula  of  Selachii,  cf.  Balfour,  "  The  Development  of 
Elasmo  branch  Fishes." — "  Journ.  of  Anat.  and  Physiol.,"  vol.  x. 
p.  517;  Plates  XX.,  XXIII. 

71  (i.  221).  Yelk-cells  of  Birds.  The  cell-like  constituent 
parts,  which  occur  in  great  number  and  variety  in  the  nutritive 
yelk  of  Birds  and  Reptiles,  as  in  most  Fishes,  are  nothing  less 
than  true  cells,  as  His  and  others  have  asserted.  This  does  not 
mean  that  in  this  matter  a  distinct  limit  everywhere  exists 
between  the  nutritive  and  the  formative  yelks,  as  in  our  oceanic 
Fish-eggs  (Figs.  42,  43,  note  70).  On  the  contrary,  originally 
(phylogenetically)  the  nutritive  yelk  originated  from  part  of  the 
entoderm. 

72  (i.  223).  Egg-cells  of  Birds.  Notwithstanding  the  large 
nutritive  yelk,  the  "after-egg  "  (metovum)  of  Birds  and  Reptiles 
is,  in  form- value,  a  single  cell.  The  very  small,  active  protoplasm 
of  the  "  tread  "  does,  however,  indeed  fall  far  short,  in  volume, 
of  the  huge  mass  of  the  yellow  yelk-ball.  The  bird's  eggs  are 
absolutely  the  largest  cells  of  the  animal  body.  Cf.  note  43,  and 
Eduard    van    Beneden,    "  Recherches   sur   la  composition  et  la 


472  NOTES. 

signification  de  l'ceuf."  Brussels,  1870.  Hubert  Ludwig,  "On 
Egg-structure  in  the  Animal  Kingdom  "  ("  Ueber  die  Eibildung 
in  Thierreicbe."     Wiirzburg,  1874). 

73  (i.  226).  Discoidal  cleavage  (Segmentatio  discoidalis)  of 
Bird's  eggs.  Cf.  Kolliker,  "  History  of  tbe  Evolution  of  Man 
and  the  Higher  Animals"  ("Entwickelungsgeschichte  des  Men- 
schen  und  der  hoheren  Thiere."  2nd  edition,  1876,  pp.  69-81  ; 
Figs.  16-22). 

74  (i.  227).  Disc-gastrula  (Blsco-gastrula)  of  Birds.  Cf. 
Rauber,  "  On  the  Place  of  the  Chick  in  the  System  of  Evolu- 
tion "  ("  Ueber  die  Stellung  des  Hiihnchens  im  Entwickelungs- 
plan").  Leipzig,  1876.  Foster  and  Balfour,  "  The  Elements  of 
Embryology."     London,  1874. 

75  (i.  231).  Bladder-gastrula  (Perigastrula)  of  Articulated 
Animals  (Arthropoda) .  Cf.  Bobretzky,  "  Russian  Essay  on  the 
Germ-history  of  Astacus  and  Pakernon."  Kiew,  1873.  Also  my 
own  article  on  the  gastrula  and  egg-cleavage. — "  Jen.  Zeitschrif t 
fiir  Naturwissenschaft."     Yol.  ix.  pp.  444-452,  Plate  VI. 

76  (i.  234).  The  Four-layer  Theory,  which  was  first  clearly 
stated  by  Baer  in  1837  ("  Entwickelungsgeschichte  der  Thiere," 
vol.  ii.  pp.  46,  68),  and  which  we  have  here  carried  out  logically, 
yet  appears  the  only  form  of  the  germ-layer  theory,  which, 
on  comparative  observation  of  all  higher  animals,  supplies  a 
universal  law  of  germination  for  all  and  at  the  same  time  meets 
the  inconsistent  reputations  of  many  observers. 

77  (i.  239).  Caspar  Friedrich  Wolff  first  indicated  the  Four- 
layer  Theory  (note  76).  Cf.  the  remarkable  sentence,  quoted  at 
vol.  i.  p.  45,  from  his  pregnant  work  on  the  formation  of  the 
intestinal  canal  (note  19). 

78  (i.  240).  The  Four  Main  Types  of  Gastrulation,  which 
are  diagrammatically  distinguished  in  Plates  II.  and  III.,  and  in 
Tables  III.  and  IV.  (vol.  i.  pp.  241,  242),  are  of  course  connected 
by  intermediate  forms.  These  are  transitions  both  between  the 
primordial  and  the  unequal  forms,  and  between  the  primordial  and 
the  superficial  forms  ;  similarly,  the  unequal  form  of  egg-cleavage 
is  connected  by  twixt-forms  with  the  discoidal  forms,  which  latter 


NOTES.  473 

is  again,  perhaps,  connected  in  the  same  way  with  the  superficial 
form. 

79  (i.  241).  The  Gastrulation  of  the  various  classes  of 
animals  has  been  far  too  little  studied  to  enable  us  thoroughly 
to  summarize  the  distribution  of  the  various  forms  within  the 
separate  classes.  Yet  it  is  already  evident  that  primordial  egg- 
cleavage  and  the  formation  of  the  Archigastrula  occur  in  the 
lowest  classes  of  each  tribe. 

80  (i.  243).  The  Rhythm  of  egg-cleavage  is  by  no  means  as 
regular  as  might  appear  from  the  four  first  examples  in  the  five 
tables.  There  are,  on  the  contrary,  many  variations,  and  not 
infrequently  an  entirely  irregular  and  very  variable  sequence  of 
numbers  occurs  (especially  in  discoided  cleavage). 

81  (i.  246).  Definition  of  the  Type.  Cf.  Gcgenbaur, 
"  Elements  of  Comparative  Anatomy,"  1874,  p.  59. 

82  (i.  246).  Types  and  Phyla.  According  to  the  prevailing 
"  Type-theory,"  the  types  of  the  animal  kingdom  are  parallel, 
and  entirely  independent ;  according  to  my  "  Gastrasa-theory," 
on  the  contrary,  they  are  divergent  tribes,  connected  at  the 
roots  ;  according  to  the  view  of  Claus  and  other  opponents,  the 
latter  is  no  essential  distinction. 

83  (i.  248).  The  one-celled  condition  of  Infusoria  entirely 
forbids  their  morphological  comparison  with  Metazoa.  Cf.  my 
article  "  On  the  Morphology  of  Infusoria  "  ("  Jen.  Zeitschrii't 
fur  Naturwissenschaft "  1873,  vol.  vii.  p.  516-568). 

84  (i.  257).  The  axes  of  the  Vertebrate  outline.  Cf.  my 
"  Promorphology  "  (Stereometry  of  Organisms).— "  Generelle 
Morphologie,"  vol.  i.  pp.  374-574.  "Singly  double-outlines" 
(Dqjleura),  p.  519.  "Bilateral-symmetrical"  forms  in  the  fourth 
signification  of  the  word. 

85  (i.  255).  The  Primitive  Vertebrate  Type,  as  it  is  repre- 
sented in  Figs.  52-56,  is  a  hypothetic  diagram,  which  is  principally 
founded  on  the  outline  of  the  Amphioxus,  but  in  which  the 
Comparative  Anatomy  of  Ascidia  and  Appendicularia  on  the 
one  side,  of  Cyclostomi  and  Selachii  on  the  other,  is  regarded. 
This  diagram  is  by  no  means  meant  to  be  an  "  exact  figure,"  but 


474  NOTES. 

a-  provisional  stage  in  the  hypothetic  reconstruction  of  the 
unknown,  long  extinct  parent-form  of  Vertebrates,  an  "Archi- 
type/' 

86  (i.  258).  Only  very  uncertain  assumptions  can  be  made 
as  to  the  sense-organs  of  the  hypothetic  parent-form,  for  these 
organs,  more  than  any  others,  have  been  subject  to  adaptations, 
and  in  Ascidia,  as  in  the  Amphioxus,  have  probably  been  much 
atrophied.  The  earliest  Vertebrates  probably  inherited  a  pair 
of  eyes  of  very  simple  character  and  a  pair  of  simple  ear- vesicles 
from  Worms. 

87  (i.  267).  The  primitive  kidneys  were  perhaps  already 
metameric  in  the  hypothetic  parent-form  of  Vertebrates,  so  that 
in  addition  to  the  two  longitudinal  main  canals  (primitive 
kidney  ducts)  numerous  transverse  tubes  (segmental  canals) 
were  connected  with  these  main  canals,  a  pair  in  each  metameron 
of  the  middle  part  of  the  body.  Perhaps  these  already  opened 
through  ciliated  funnels  into  the  body-cavity  (coeloma),  as  is 
now  the  case  in  Annelids,  and,  according  to  Balfour,  in  the 
embryos  of  Selachii.  Cf.  Balfour,  "  Development  of  Elasmo- 
branch  Fishes." — "Quarterly  Journal  of  Microscopical  Science." 
New  Series,  vol.  xiv.  p.  323 ;  "  Journal  of  Anat.  and  Physiol." 
vol.  x. 

88  (i.  273).  The  germination  of  Primitive  Vertebrates.  Cf. 
with  Table  VI.,  Table  VII.  (vol.  i.  p.  327),  Table  XI.  (p.  467); 
also  the  diagrammatic  figures  in  Plates  IV.  and  V.  with  explana- 
tion (p.  321). 

89  (i.  276).  The  Germ-forms  of  the  earliest  Vertebrates,  as 
they  are  represented  in  diagrammatic  cross  sections  in  Figs. 
62-69,  can  only,  of  course,  be  approximately  guessed,  and  with 
the  aid  of  Comparative  Anatomy  and  Ontogeny.  These 
hypothetic  diagrams,  therefore,  by  no  means  claim  to  be  ac- 
cepted dogmatically,  any  more  than  do  those  in  Figs.  52-56. 
(Cf.  note  85.) 

90  (i.  280).  Main  incidents  in  Vertebrate  germination.  Of 
the  main  palingenetic  incidents  here  enumerated,  perhaps  the 
sixth,    ninth,    and    tenth    originally    occurred    in    a    very    dif- 


NOTES.  475 

ferent  form.      The  other  seven  now   appear  to  be  pretty   well 
established. 

01  (i.  285).  The  flat  germ-disc  of  Birds,  which  even  now,  in 
the  opinion  of  most  embryologists,  represents  the  first  starting- 
point  in  the  formation  of  the  embryo,  and  to  which  all  other 
germ-forms  have  been  referred,  is,  on  the  contrary,  a  late  and 
much  modified  germ-form,  which  has  arisen  in  consequence  of 
the  extension  of  the  gastrula  over  the  greatly  enlarging  nutritive 
yelk. 

92  (i.  289).  Site  of  Fertilization.  In  Man,  as  in  other 
Mammals,  fertilization  of  the  eggs  probably  usually  takes  place 
in  the  oviduct :  here,  the  eggs  which,  at  the  rupture  of  the 
Graafian  follicles,  have  emerged  from  the  female  ovary  and 
passed  into  the  outer  opening  of  the  oviduct,  meet  with  the 
active  sperm-cells  of  the  male  seed,  which,  during  copulation, 
penetrated  into  the  uterus,  and  from  there  passed  into  the  inner 
opening  of  the  oviduct.  Rarely,  fertilization  occurs  even  on  the 
ovary,  or  not  till  within  the  uterus.     (Cf.  Chapter  XXV.) 

93  (i.  293).  The  origin  of  the  mesoderm  in  Mammals,  as  in 
other  animals,  is,  at  present,  among  the  most  obscure  and  con- 
tested points  of  Ontogeny.  Remak,  Balfour,  and  others  derive 
it  from  the  entoderm,  Kolliker  and  others  from  the  exoderm. 
Waldeyer,  His,  and  others  assert  that  both  primary  germ-layers 
take  part  in  the  formation  of  the  mesoderm.  The  last  assump- 
tion is,  I  believe,  correct.     (Cf.  notes  76,  77.) 

94  (i.  297).  The  Germ-shield  (Notasiris).  The  ordinary 
view,  that  the  germ-shield  (=  Remak's  "  Doppelschild  ")  is  the 
earliest  rudiment  of  the  actual  embryo,  results  in  many  erroneous 
conclusions.  It  is,  therefore,  necessary  to  point  out  especially 
that  the  germ-shield  represents  the  first  well-defined  central 
dorsal  part  of  the  embryo. 

95  (i.  317).  Body  Wall  and  Intestinal  Wall.  The  morpho- 
logical distinction  between  the  body  wall  and  the  intestinal  wall, 
certainly  primordial,  is  probably  referable  to  the  simple  primary 
germ-layers  of  the  Gastraja.  If  the  skin-fibrous  layer  is  derived 
from   the   exoderm,  and   the   intestinal-fibrous  layer   from    the 


4/6  NOTES. 

entoderm,  this  most  simply  explains  the  progressive  development 
of  this  distinction,  which  may  be  traced  through  the  series  of 
Worms,  and  np  to  Vertebrates. 

96  (i.  320).  Palingenetic  and  Kenogenetic  germination.  In 
the  germ-history  of  Vertebrates  no  clear  conception  of  the 
embryological  process  has  yet  been  attained,  because  all  authors 
have  started  from  the  higher  Vertebrates  (usually  from  the 
Chick)  and  have  assumed  that  the  form  of  evolution  occurring 
in  this  case  is  original  and  typical.  It  is  only  since  the  germ- 
history  of  the  Amphioxus  has  taught  us  the  palingenetic,  really 
original  form  of  germination  of  Vertebrate  organisms,  that  we 
have  been  enabled,  by  Comparative  Ontogeny  (and  especially  by 
the  principles  of  the  Gastra?a  theory),  rightly  to  understand  and 
to  explain  phylogenetically  the  kenogenetic  forms  of  germination 
of  higher  Vertebrates. 

97  (i.  321).  The  Diagrams  in  Plates  IV.  and  V.  are  as  simple 
and  abstract  as  possible,  in  order  to  render  the  desired  general 
explanation  as  easy  as  possible. 

98  (i.  346).  Primitive  Vertebras  and  Metamera.  For  the 
right  conception  of  "  primitive  vertebral  "  structure  it  is  espe- 
cially necessary  to  point  out  that  the  primitive  vertebrae  are 
much  more  than  their  name  indicates.  They  must,  in  fact,  be 
conceived  as  individual,  consecutive  sections  of  the  trunk, 
which  have  arisen  one  after  the  other,  as  true  "  metamera,"  or 
consecutive  pieces  ("  Generelle  Morphologie,"  vol.  i.  p.  312). 
Each  primitive  vertebra  of  a  Vertebrate,  like  each  trunk-segment 
or  metameron  of  an  Annelid  or  Arthropod,  contains  all  the 
essential,  morphological  constituent  parts,  characteristic  of  the 
corresponding  animal-tribe. 

99  (i.  349).  Origin  of  the  Primitive  Vertebra?.  My  concep- 
tion of  these  as  individual,  morphological  "consecutive  pieces," 
which,  like  the  metamera  of  Cestods  and  Annelids,  have  arisen 
by  terminal  budding  from  a  single  unarticulated  piece,  has  been 
much  attacked.  I  therefore  emphatically  remark  that  I  only 
understand  this  process  in  the  widest  sense.  In  both  cases  there 
is  certainly  a  reproduction  of  individual,  like  parts,  which  have 
originated  (in  time  and  space)  consecutively. 


NOTES. 


477 


100  (i.  3G1).  The  agreement  among  the  germ-forms  of 
various  Mammals  is  instructive  especially  because  it  shows  us 
how,  by  diversity  in  the  mode  of  evolution,  the  most  diverse 
structures  can  originate  from  one  and  the  same  form.  As  we 
actually  see  this  in  germ-forms,  we  may  hypothetically  assume 
the  same  to  have  occurred  among  tribe-forms.  Moreover, 
this  agreement  is  never  absolute  identity,  but  always  only 
the  very  greatest  similarity.  Even  the  germs  of  the  various 
individuals  of  a  species  are  never  actually  identical. 

101  (i.  366).  The  law  of  the  ontogenetic  connection  of 
systematically  allied  animal-forms  has  many  apparent  exceptions. 
These  are,  however,  fully  explained  by  the  adaptation  of  the 
gorm  to  kenogenetic  conditions  of  existence.  Where  the  palin- 
genetic  form  of  evolution  of  the  germ  has  been  accurately 
transmitted  by  heredity,  that  law  is  always  in  force.  Cf.  Fritz 
Miillcr,  "Fur  Darwin  "  (note  111). 

102  (i.  367).  Earliest  human  germs.  Cf.  Kolliker,  "  History 
of  the  Evolution  of  Man  "  ("  Entwickelungsgeschichte  des  Men- 
schen."  2nd  edition,  1876,  pp.  303-319).  Also  Eckcr,  "Iconcs 
physiologicue."  Leipzig,  1859.  Plates  XXV.-XXXI.  The 
earliest  human  germs  which  have  yet  been  certainly  recognized, 
were  from  twelve  to  fourteen  days  old,  and  were  observed  by 
Prof.  Allen  Thomson,  of  Glasgow.  Xo  opportunity  has  ever 
occurred  for  the  observation  of  earlier  germs. 

103  (i.  369).  Human  germs  of  three  weeks  (twenty  to  twenty- 
one  days)  exhibit  in  their  whole  structure  that  phylogenetic  sta^e 
of  evolution  which,  among  extant  Vertebrates,  is  represented  by 
the  Cyclostomi  (Lampreys  and  Hags,  vol.  ii.  p.  103),  and  which 
must  be  referable  to  extinct  Monorhine  ancestors  of  similar 
structure. 

104  (i.  370).  Human  germs  of  four  weeks  (twenty-five  to 
thirty  days),  on  the  whole,  exhibit  in  their  whole  structure  that 
phylogenetic  stage  of  evolution,  which  is  exhibited  in  Sharks 
and  Rays,  among  extant  Vertebrates,  and  which  is  referable  to 
similar  extinct  Primitive  Fish  ancestors  (Proselachli).  Of  course 
this  comparison  ia  affected  by  various  kenogenetic  modifications 


478  NOTES. 

(both   heterotopic   and  heterochronic),  just   as   in   the   former. 
(Cf.  note  108.) 

105  (i.  374).  The  nose  of  Nosed-apes  is  much  more  different 
from  that  of  other  Apes  than  from  that  of  Man.  Moreover, 
even  the  extreme  variety  and  variability  in  the  external  form 
of  the  human  nose  shows  how  small  is  the  morphological  value 
of  this  organ,  so  important  to  the  physiognomy. 

106  (i.  383).  The  bladder-like  form  of  the  human  Allantois. 
Cf.  W.  Krause,  "  On  the  Allantois  in  Man  "  ("  Ueber  die  Allan- 
tois des  Menschen." — "Archiv  fur  Anat.  u.  Physiol.,"  1875,  p.  215, 
Plate  VI.). 

107  (i.  400).  The  navel-cord  (funiculus  umhUicalis),  like 
the  placenta,  is  an  organ  shared  by  Man  exclusively  with  Pla- 
cental Animals.  Cf.  Chap.  XIX.  pp.  155-168,  and  Figs.  200,  201. 
On  the  more  minute  structure  of  this  organ,  and  on  the  special 
features  of  the  embryonic  blood-circulation,  cf.  Kolliker,  "  His- 
tory of  the  Evolution  of  Man."     2nd  edition,  1876,  pp.  319-363. 

108  (i.  401).  The  Kenogeny  of  Man.  In  pointing  out  the 
phylogenetic  significance  of  the  separate  incidents  and  periods  of 
human  germ-history,  and  in  explaining  them  by  reference  to  cor- 
responding processes  and  stages  in  the  tribal  history  of  our  animal 
ancestors,  we  must  always  bear  in  mind  that  in  Man,  as  in  all 
higher  animals,  the  original  palingenetic  cause  of  germination 
has  undergone  much  kenogenetic  modification  in  consequence  of 
many  adaptations  to  the  very  various  conditions  of  embryonic 
life,  that  it  has  thus  been  much  violated  and  contracted.  The 
higher  the  organism  develops,  the  more  are  especially  these 
earliest  stages  of  evolution  abbreviated. 

109  (i.  404).  The  sections  of  human  germ -history,  of  which 
only  four  larger  and  ten  smaller  are  mentioned  here  in  reference 
to  their  phylogenetic  significance,  allow  of  much  more  division 
if  their  compai'ative  Ontogeny  is  minutely  examined.  This 
phylogenetic  significance  may  also  be  very  well  explained  with 
fitting  reference  to  kenogenetic  displacements  in  place  and  time 
(vol.  i.  p.  13). 

110  (i.  405).  Figures  of   human  embryos   in   all    stages  of 


notes.  479 

£crm-history  were  given  in  very  beautiful  detail  by  M.  P.  Erdl 
thirty  years  ago  :  "  The  Evolution  of  Man,  and  of  the  Chick  in 
the  Egg"  ("Die  Entwiekelung  des  Menschen,  uud  des  Hiihnchens 
im  Ei."     Leipzig,  1845). 

111  (i.  409).  Fritz  Miiller,  "Fur  Darwin."  Leipzig,  1864. 
A  very  excellent  little  book,  in  which  the  modification  of  the 
fundamental  law  of  Biogeny  (with  reference  to  the  Phylogeny  of 
Crustacea)  are  explained  for  the  first  time. 

112  (i.  413).  The  Method  of  Phylogeny  is  of  the  same 
morphological  value  as  the  well-known  method  of  Geology,  and 
may,  therefore,  claim  exactly  the  same  scientific  acceptation. 
Cf.  the  excellent  discourse  by  Eduard  Strasburger,  "On  the 
Importance  of  Phylogenetic  Methods  in  the  Study  of  Living 
Beino-s." — "Jenaische  Zeitschrift  fur  Naturwissenschaft,"  1874, 
vol.  viii.  p.  56. 

113  (i.  415).  Johannes  Miiller,  "  On  the  Structure  and  Vital 
Phenomena  of  Amphioxus  lanceolatus." — Transactions  of  the 
Berlin  Academy,  1844. 

114  (i.  415).  Recent  works  on  the  Amphioxus.  W.  Rolph 
and  E.  Ray  Lankester  especially  have  recently  added  to  our 
knowledge  of  the  organology  of  the  Amphioxus,  Wilhelm  Miiller 
and  P.  Langerhans  to  that  of  its  histology.  The  literature  of 
this  subject  is  fully  represented  by  W.  Rolph,  in  his  "Researches 
into  the  Structure  of  the  Amphioxus"  ("  Untersuchungen  fiber 
den  Bau  des  Amphioxus." — "  Morpholog.  Jahrb.,"  vol.  ii.  p.  87, 
Plates  V.  and  VII.),  and  in  P.  Langerhans,  "  On  the  Anatomy  of 
the  Amphioxus"  ("Zur  Anatomie  des  Amphioxus." — "  Archiv. 
fur  Mikr.  Anat,,"  vol.  xii.  p.  200,  Plates  XII.-XV). 

115  (i.  416).  Acrania  and  Craniota.  The  separation  of 
Vertebrates  into  Skull-less  Animals  (Acrania)  and  Skulled 
Animals  (Craniota),  which  I  fix*st  indicated  in  1866  in  my 
"  Genci'elle  Morphologie,"  appears  to  me  absolutely  essential  for 
the  phylogenetic  explanation  of  the  Vertebrate-tribe. 

116  (i.  428).  Max  Schultzo,  "History  of  the  Evolution  of 
Petromyzon"  ("Entwickelungsgeschichte  von  Pctromyzon."  Haar- 
lem, 1856).  The  Ontogeny  of  the  Hags,  which  promises  very 
important  results,  is  yet,  unfortunately,  entirely  unknown. 


4§0  NOTES. 

117  (i.  430).  Savigny,  "Memoires  sur  les  Animaux  sans 
Vertebres."  Vol.  ii.,  Ascidies,  1816.  Griard,  "  Recherches  sur 
les  Synascidies." — "Archives  de  Zoologie  Experirnentale,"  vol.  i., 
1872. 

118  (i.  435).  Sjn-ascidia  and  Echinoderms.  The  Corm-theory 
of  Echinoderms,  which  I  explained  in  1866  ("  Generelle  Mor- 
phologic," vol.  ii.  p.  Ixiii),  and  which  has  been  much  attacked  as 
"  paradoxical,"  is  as  yet  the  sole  theory  attempting  the  genetic 
explanation  of  this  remarkable  group  of  animals. 

119  (i.  442).  Kowalevsky,  "History  of  the  Evolution  of  the 
Amphioxus  and  of  Simple  Ascidians"  ("  Memoires  de  l'Acad.  de 
S.  Petersbourg."     7  Serie.     Tom.  x.  and  xi.     1867-8). 

120  (i.  450).  The  metameric  structure  of  the  Amphioxus 
which  is  indicated  in  its  nerve  and  muscle  systems,  undoubtedly 
shows  that  the  notochord  exists  in  Vertebrates  previous  to  their 
metameric  structure,  and  consequently  that  it  is  inherited  from 
unarticulated  Chorda  Animals. 

121  (i.  454).  The  Metamorphosis  of  the  Amphioxus,  through 
which  the  larva  passes  into  the  adult  form,  is  not  yet  fully 
known  in  all  its  details.  This  does  not,  however,  affect  the 
extraordinarily  important  bearing  of  the  thoroughly  known, 
earliest  incidents  in  its  germination  on  the  palingenesis  of  Verte- 
brates. 

122  (i.  455).  Fertilization  of  Ascidia  (Phallusia  mammillata), 
Eduard  Strasburger,  "  On  Cell-structure  and  Cell-division,  with 
Studies  of  Fertilization."  2nd  edition.  Jena,  1876,  p.  306, 
Plate  VIII. 

123  (i.  462).  Kupfftr.  The  tribal  relation  of  Ascidia  to 
Vertebrates  ("Archiv  fur  Mikros.  Anat.,"  1870,  vol.  vi.  pp. 
115-170).  Oscar  Hertwig,  "  Researches  into  the  Structure  and 
Evolution  of  the  Cellulose  Mantles  of  Tunicata "  ("  Untersu- 
chungen  iiber  den  Bau  und  die  Entwickelung  des  Cellulose- 
Mantels  der  Tunicaten").  Richard  Hertwig,  "Contribution  to 
Knowledge  of  Ascidian  Structure"  ("  Beitriige  zur  Kenntniss 
des  Baues  der  Ascidien." — "  Jenaische  Zeitschrift  fur  Naturwis- 
senschaft,"  1873,  vol.  vii.). 


NOTES.  48 1 

124  (i.  46-1).  The  Phylogenetic  Importance  of  the  Amphi- 
oxus  cannot  be  too  highly  insisted  on.  Without  knowledge  of 
its  Anatomy  and  Ontogeny,  the  origin  of  Vertebrates  would  be 
entirely  dubious,  and  their  descent  from  Worms  would  appear 
incredible. 

125  (i.  467).  The  Ontogenetic  Cell-pedigree,  as  it  is  repre- 
sented, with  reference  to  the  Amphioxus,  in  Table  XL,  probably 
holds  good,  in  its  most  important  features,  for  all  Vertebrates, 
and,  therefore,  also  for  Man.  For,  more  than  any  other  form, 
the  Amphioxus  by  strict  Heredity  has  accurately  retained  its 
Palingenesis.  This  histogenetic  cell-pedigree  is  apparently  well 
established  as  regards  most  and  the  chief  features  ;  on  the  other 
hand,  it  yet  appears  doubtful  with  regard  to  the  origin  of  the 
primitive  kidneys,  the  testes,  and  ovaries. 

126  (ii.  4).  Milne-Edwards,  "Lecons  sur  la  Physiologic 
Comparee,"  vol.  ix. 

127  (ii.  6).  Eternity  of  Organic  Life.  According  to  the 
monistic  view,  organic  life  is  a  further  form  of  evolution  of  the 
inorganic  word-processes,  and  had  a  beginning  in  time  on  our 
planet.  In  opposition  to  this,  A.  Fechner,  among  others,  in  his 
"Thoughts  on  the  Creation  and  Evolution  of  Organisms,"  has 
stated  certain  opposed  "  kosmorganic  phantasys  "  which  appear 
entirely  irreconcilable  with  the  ontogenetic  facts  given  here. 

128  (ii.  18).  Bernhard  Cotta  ("  Geologie  der  Gegenwart," 
1866;  4th  edition,  1874)  and  Karl  Zittel("Aus  der  Urzeit;" 
Miiuchen,  1875,  2nd  edition)  have  made  some  excellent  remarks 
on  the  duration  and  the  whole  course  of  the  organic  history  of 
the  world. 

129  (ii.  21).  August  Schleicher,  "The  Darwinian  Theory 
:ind  Philology"  ("Die  Darwin'sche  Theorie  und  die  Sprach- 
wissenschaft."     Weimar,  1863.     2nd  edition,  1873). 

130  (ii.  25).  At  first  sight,  most  polyphylotic  hypotheses 
appear  more  simple  and  easy  than  do  monophyletic,  but  the 
former  always  present  more  difficulties  the  more  they  are 
considered. 

131  (ii.   25).    Those   physiologists    who    desire   an    experi- 


4^2  NOTES. 

mental  proof  of  the  theory  of  descent,  merely  thereby  pi*ove  their 
extraordinary  ignorance  of  the  morphological  scientific  facts  re- 
lating to  this  matter. 

132  (ii.  30).  Spontaneous  generation. — "  Generelle  Mor- 
phologie,"  vol.  i.  pp.  167-190.  "  Monera  and  Spontaneous  Gene- 
ration."— "Jenaische  Zeitschrift  fiir  Naturwissenschaft,"  1871, 
vol.  vi.  pp.  37-42. 

133  (ii.  33).  The  Absence  of  Organs  in  Monera.  In  saying 
that  Monera  are  "organisms  without  organs,"  we  understand  the 
definition  of  organs  in  a  morphological  sense.  In  a  physiological 
sense,  on  the  other  hand,  we  may  call  the  variable  plasson- 
processcs  of  the  body  of  the  Moneron  the  "  yseudo^oclia  "  organs. 

134  (ii.  36).  Induction  and  Deduction  in  Anthropogeny. 
"  Generelle  Morphologic,"  vol.  i.  pp.  79-88 ;  vol.  ii.  p.  427. 
"  History  of  Creation,"  vol.  ii.  p.  357. 

135  (ii.  42).  Animal  Ancestors  of  Man.  The  number  of 
species  (or,  more  accurately,  form-stages,  which  are  distinguished 
as  "  species  ")  must,  in  the  human  ancestral  line  (in  the  course  of 
many  millions  of  years !),  have  amounted  to  many  thousands ; 
the  number  of  genera  to  many  hundreds. 

136  (ii.  47).  Following  Elsberg,  we  give  the  name  of  "plas- 
tidules"  to  the  "molecules  of  plasson,"  to  the  smallest  like  parts 
of  that  albuminous  substance  which,  according  to  the  "  plastid- 
theory,"  is  the  material  substratum  of  all  the  active  phenomena 
of  life.  Cf.  my  work  on  "  The  Perigenesis  of  Plastidules " 
("Perigenesis  der  Plastidule  oder  Well enzcu gun g  der  Lebens- 
theilchen."  Berlin,  1876).  This  is  an  attempt  to  explain 
mechanically  the  elementary  processes  of  evolution. 

137  (ii.  49).  Bathybius  and  the  free  protoplasm  of  ocean 
depths.  Cf.  my  "  Studies  on  Monera  and  other  Protista." 
Leipzig,  1870,  p.  86.  The  most  recent  observations  on  living 
Bathybius  are  those  of  Dr.  Emil  Bcssel,  who  found  this  form  on 
the  coast  of  Greenland  (in  Smith's  Sound),  at  a  depth  of  about 
550  ft.  He  noticed  very  active  amoeboid  movements  in  them, 
as  well  as  the  assumption  of  foreign  particles  (carmine,  etc.). 
"It  consists  of  nearly  pure  protoplasm,  tinged  most  intensely  by 


NOTES.  483 

a  solution  of  carmine  in  ammonia.  It  contains  fine  gray  granules 
of  considerable  refracting  power,  and  besides  the  latter  a  great 
number  of  oleaginous  drops,  soluble  in  ether.  It  manifests  very 
marked  amoeboid  motions,  and  takes  up  particles  of  carmine,  etc." 
— Packard,  "Life  Histories  of  Animals,  including  Man."  New 
York,  1876. 

138  (ii.  50).  The  Philosopbical  Importance  of  Monera  in 
explaining  the  most  obscure  biological  questions  cannot  be 
sufficiently  emphasized.  Monograph  of  Monera. — "  Jenaische 
Zeitschrift  fur  Naturwissenschaft,"  vol.  iv.,  1868,  p.  64. 

139  (ii.  54).  The  Nature  and  Significance  of  the  Egg-cell  can 
only  be  philosophically  understood  by  means,  of  phylogenetic 
examination. 

140  (ii.  58).  Synamceba.  Cienkowski,  "  On  the  Structure 
and  Evolution  of  Labyrinthula  "  ("Uber  den  Bau  und  die  Entwic- 
kelung  der  Labyrinthuleen." — Arch,  fur  Mikrosk.  Anat.,  1870, 
vol.  iii.  p.  274).     Hertwig,  "  Microgromia  Socialis." — Ibid. 

141  (ii.  61).  Catallacta,  a  new  Protista-group  (Mayo  splicer  a 
planula).  See  "  Jenaische  Zeitschrift  fur  Naturwissenschaft," 
vol.  vi.,  1871,  p.  1. 

142  (ii.  66).  Haliphysema  and  Gastrophysema.  Extant 
Gastrasads.  See  "Jenaische  Zeitschrift  fiir  Naturwissenschaft," 
vol.  xi.,  1876,  p.  1,  Plates  I.-VI. 

143  (ii.  70).  The  five  first  stages  in  the  evolution  of  the 
animal  body,  which  are  compared  in  Table  XVII.,  and  which 
are  common  to  Man  and  all  higher  Animals,  are  established 
beyond  all  doubt  as  existing  in  the  Ontogeny  of  most  extant 
animals.  As  Comparative  Anatomy  shows  that  corresponding 
form-stages  yet  exist  in  the  system  of  the  lower  animals,  we 
may  assume,  in  accordance  with  the  fundamental  law  of  Biogeny, 
that  similar  forms  existed  phylogenetically  as  most  important 
ancestral  forms. 

144  (ii.  77).  On  the  distinction  of  the  axes,  and  on  the 
geometric  outline  of  the  animal  body,  see  "  Promorphologie " 
("  Generelle  Morphologie,"  vol.  i.  pp.  374-574). 

145  (ii.  87).  The  hermaphrodite  structure   of   our    ancestral 


484  NOTES. 

series  was  perhaps  transmitted  from  the  Chorda  Animals  even  as 
far  as  the  lower  stages  of  Vertebrate  ancestors.   Cf.  Chapter  XXV. 

146  (ii.  89).  I  am  inclined  to  regard  the  Appendicularia  as 
living  Chorda  Animals  of  the  present  day;  they  are  the  only 
Invertebrates  permanently  possessing  a  notochord,  and  thus,  as 
by  many  other  peculiarities,  distinguished  from  genuine  Tuni- 
cates. 

147  (ii.  105).  Metamorphosis  of  Lampreys.  That  the  blind 
Ammoccetes  change  into  Petromyzon  was  known  two  hundred 
years  ago  (1666)  to  the  fisherman  Leonhard  Baldner  of  Stras- 
burg ;  but  this  observation  remained  unrecognized,  and  the 
modification  was  first  discovered  by  August  Miiller  in  1854 
("  Archiv  fiir  Anat.,"  1856,  p.  325).  Cf.  Siebold,  "The  Fresh- 
water Fishes  of  Central  Europe"  ("Die  Siisswasserfische  von 
Mittel-Europa,"  1863). 

148  (ii.  114).  Selachii  as  Primitive  Fishes.  The  old  disputes 
as  to  the  systematic  position  and  kindred  of  Selachii  were  first 
definitely  settled  by  Gegenbaur,  in  the  introduction  to  his  classical 
work  on  "  The  Head-skeleton  of  Selachii." 

149  (ii.  118).  Gerard  Krefft,  "  Description  of  a  Gigantic  Am- 
phibian ;  "  and  Albert  Giinther,  "  Ceratodus,  and  its  Systematic 
Position." — "Archiv  fiir  Naturgeschichte,"  37,  1871,  vol.  i.  p. 
321  ;  also  "Phil.  Trans.,"  1871,  Part  II.  p.  511,  etc. 

150  (ii.  129).  The  duration  of  metamorphosis  of  Amphibia 
varies  much  in  the  different  forms  of  Frogs  and  Toads,  the  whole 
forming  a  complete  phylogenetic  series  from  the  original,  quite 
complete  form,  to  the  later,  much  shortened  and  vitiated  heredity 
of  modification. 

151  (ii.  129).  "All  the  histological  features  of  the  Land 
Salamander  (Salamandra  maculata)  force  the  impression  that  it 
belongs  to  an  entirely  different  epoch  of  terrestrial  life  than  that 
of  the  Water  Salamander  (Triton),  externally  so  similar." — Robert 
Remak  ("  Entvvickelung  der  Wirbelthiere,"  p.  117). 

152  (ii.  130).  Siredon  and  Amblystoma.  Very  various  views 
have  lately  been  expressed  as  to  the  phylogenetic  significance  to 
be  attributed  to  the  much-discussed  modification  of  the  Mexican 


NOTES.  485 

Axolotl  into  an  Amblystoma.  Cf.  on  this  subject  especially 
August  "VVeismann,  in  "  Zeitsch.  fur  vvissensch.  Zoologie,"  vol. 
xxv.,  Sup.,  pp.  297-334 

153  (ii.  131).  The  Leaf-frog  of  Martinique  (Ri/lodcs  mar- 
tinicensis)  loses  its  gills  on  the  seventh  day,  its  tail  and  yelk-sac 
on  the  eighth  day  of  egg-life.  On  the  ninth  or  tenth  day  after 
fertilization  the  complete  frog  emerges  from  the  egg. — Bavay, 
"Sur  l'Hylodes  Martinicensis  et  ses  Metamorphoses."  "Journal, 
de  Zool.  par  Grevais,"  vol.  ii.  1873,  p.  13. 

154  (ii.  133).  "  Homo  diluvii  testis  "  =  Andi-ias  Scheuchzeri. 
"  Sad  bone  of  an  ancient  evil-doer ;  Soften,  stone,  the  heart  of 
the  new  children  of  evil "  (Diaconus  Miller).  Quenstedt. 
"Formerly  and  Now  "  ("  Sonst  und  Jetzt,"  1856,  p.  239). 

155  (ii.  133).  The  Amnion-structure  of  the  three  higher 
Vertebrate-classes,  wanting  in  all  lower  Vertebrates,  has  no 
connection  with  the  similar,  but  independently  acquired  Amnion- 
structure  (analogous,  but  not  homologous)  of  higher  Articu- 
lated Animals  (Arthropod*  1). 

156  (ii.  138).  The  former  existence  of  a  Protamnion,  the 
common  parent-form  of  all  Amniota,  is  undoubtedly  shown  by 
the  Comparative  Anatomy  and  Ontogeny  of  Reptiles,  Birds,  and 
Mammals.  No  fossil  remains  of  such  a  Protamnion  have,  how- 
ever, yet  been  discovered.  They  must  be  sought  in  the  Permian 
or  Carboniferous  formation. 

157  (ii.  147).  The  former  organisation  of  the  Promammalia 
may  be  hypothetically  reconstructed  from  the  Comparative 
Anatomy  of  the  Salamander,  Lizards,  and  Beaked  Animals 
(OrnithorJn/ncliiis). 

158  (ii.  153).  The  Didelphic  ancestors  of  Man  may  have  been 
externally  very  different  from  all  known  Pouched  Animals  (Mar- 
supialia),  but  possessed  all  the  essential  internal  characters  of 
Marsupialia. 

159  (ii.  163).  The  phylogenetic  of  the  Semi-apes,  as  the 
primaeval  placental  parent-group,  is  not  influenced  by  our  ignor- 
ance of  any  fossil  Prosimiae,  for  it  is  never  safe  to  estimate 
palaeontological  facts  as  negative,  but  only  as  positive. 


486  NOTES. 

160  (ii.  168).  On  the  structure  of  the  Decidua  very  various 
theories  have  been  given.  Cf.  Kolliker,  "History  of  the  Evolution 
of  Man "  ("  Entwickelungsgeschichte  des  Menschen."  2nd 
edition,  187] ,  pp.  319-376).  Ercolani  (Giambattista),  "  Sul  pro- 
cesso  formativo  della  placenta."  Bologna,  1870.  "  Le  glandole 
otricolari  del'utero."  Bologna,  1868,  1873.  Huxley,  "Lectures 
on  the  Elements  of  Comparative  Anatomy,"  1864,  pp.  101-112. 

161  (ii.  172).  Huxley,  "  Anatomy  of  Vertebrates,"  1873, 
p.  382.  Previously  Huxley  had  separated  the  "  Primates  "  into 
seven  families  of  nearly  equal  systematic  value.  (See  "Man's 
Place,"  etc.,  p.  119.) 

162  (ii.  179).  Darwin.  Sexual  selection  in  Apes  and  Man. — 
"  Descent  of  Man,"  vol.  ii.  pp.  210-355. 

163  (ii.  180).  Man-like  Holy  Apes.  Of  all  Apes,  some  Holy 
Apes  (Semnopithecus)  most  resemble  Man,  in  the  form  of  their 
nose  and  the  character  of  their  hair  (both  that  on  the  head  and 
that  on  the  beard). — Darwin,  "  Descent  of  Man,"  vol.  i.  p.  335 ; 
vol.  ii.  p.  172. 

164  (ii.  182).  Friedrich  Miiller  ("  Allgemeine  Ethnographic" 
Vienna,  1873,  p.  29),  on  the  supposed  age  of  man.  Families  of 
languages  (pp.  5,  15,  etc.). 

165  (ii.  183).  The  plate  (XV.)  representing  the  migrations, 
given  in  the  "History  of  Creation,"  merely  claims  the  value  of 
a  first  attempt,  is  an  hypothetic  sketch,  as  I  there  expressly  said, 
and  as,  in  consequence  of  repeated  attacks,  I  must  here  insist. 

166  (ii.  201).  The  Leather-plate.  The  phylogenetic  distinction 
of  a  special  leather-plate,  the  outermost  lamella  separating  from 
the  skin-fibrous  layer,  is  justified  by  Comparative  Anatomy. 

167  (ii.  204).  Milk-glands.  Huss,  "Contributions  to  the 
History  of  the  Evolution  of  the  Milk-glands"  ("Beitrage  zur 
Entwickelungsgeschichte  der  Milchdriisen  ")  ;  and  Gegenbaur, 
"  On  the  Milk-gland  Papilke "  ("  Jenaischc  Zeitschvift  fur 
Naturwissenschaft,"  1873,  vol.  vii.  pp.  176,  204). 

168  (ii.  208).  On  the  hairy  covering  of  Man  and  Apes,  see 
Darwin,  "Descent  of  Man,"  vol.  i.  pp.  20,  167,  180;  vol.  ii. 
pp.  280,  298,  335,  etc. 


NOTES.  48; 

169  (ii.  217).  Dorsal  side  and  ventral  sides  are  homologous 
in  Vertebrates,  Articulated  Animals  (Arthropod a),  Soft-bodied 
Animals  (Mollusca),  and  Worms,  so  that  the  dorsal  marrow  and 
the  ventral  marrow  are  not  comparable.  Cf.  Gegenbaur,  "Morph. 
Jahrbuch,"  vol.  i.  pp.  5,  6. 

170  (ii.  228).  The  unknown  ontogenetic  origin  of  the  sym- 
pathetic nerve-system  must  probably,  for  phylogenetic  reasons, 
be  sought  chiefly  in  the  intestinal  layer,  not  in  the  skin-layer. 

171  (ii.  248).  On  the  cavities  connected  with  the  nose,  see 
Gegenbaur,  "  Elements  of  Comparative  Anatomy,"  p.  580. 

172  (ii.  260).  The  analogies  in  the  germination  of  the  higher 
sense  organs  were  rightly  grasped  even  by  the  earlier  natural 
philosophers.  The  first  more  accurate  sketches  of  the  very 
obscure  germ-history  of  the  sense-organs,  especially  of  the  eye 
and  ear,  were  given  (1830)  by  Emil  Huschke,  of  Jena  (Isis, 
Meckel's  Archiv,  etc.). 

173  (ii.  .265).  Hasse,  "  Anatomical  Studies "  ("  Anatomische 
Studien  "),  chiefly  of  the  organ  of  hearing.     Leipzig,  1873. 

174  (ii.  269).  Johannes  Rathke,  "On  the  Gill-apparatus  and 
the  Tongue-bone "  ("  Ueber  den  Kiemen-apparat  und  des 
Zungenbein,"  1832).  Gegenbaur,  "On  the  Head-skeleton  of 
Sclachii,"  1872.     (See  note  124.) 

175  (ii.  272).  On  the  Rudimentary  Ear-shell  of  Man,  cf. 
Darwin,  "  Descent  of  Man,"  vol.  i.  pp.  17-19. 

176  (ii.  276).  Scarcely  anywhere  does  Comparative  Anatomy 
prove  its  high  morphological  value  as  with  reference  to  the 
skeleton  of  Vertebrates:  in  this  matter  it  accomplishes  much 
more  than  Ontogeny.  There  is  all  the  more  reason  to  insist  on 
this  here,  as  Goctte,  in  his  gigantic  history  of  the  evolution  of 
Bombinator,  has  recently  denied  all  scientific  value  to  Com- 
parative Anatomy,  and  asserted  that  Morphology  is  explained 
solely  by  Ontogeny.  Cf.  my  "Aims  and  Methods  of  the  Recent 
History  of  Evolution  "  ("  Ziele  und  Wege  der  heutigen  Eut- 
wickelungsgeschichte,"  1875,  p.  52,  etc.). 

177  (ii.  283).  The  Human  Tail,  like  all  other  rudimentary 
organs,  is  very  variable  in  point  of  size  and  development.     In 

H 


488  NOTES. 

rare  cases  it  remains  permanently,  projecting  freely :  usually  it 
disappears  at  an  early  period,  as  in  Anthropoid  Apes. 

178  (ii.  284).  On  the  Number  of  Vertebra?  in  different  Mam- 
mals,  cf.  Cnvier,  "Lecons  d'Anatomie  Comparee."  2nd  edition, 
tomei.,  1835,  p.  177.' 

179  (ii.  293).  On  the  earlier  Skull-theory  of  Goethe  and  Oken, 
cf.  Virchow,  "  Goethe  as  a  Naturalist "  ("  Goethe  als  Natur- 
forscher,"  1861,  p.  103). 

180  (ii  295.).  Karl  Gegenbaur,  "The  Head-skeleton  of 
Selachii"  ("Das  Kopfskelet  der  Selachier").  As  the  foundation 
of  a  study  of  the  head-skeleton  of  Vertebrates  (1872). 

181  (ii.  301).  Karl  Gegenbaur,  "On  the  Archipterygium." 
— "Jenaiscbe  Zeitschrift  fur  Naturwissenschaft,"  vol.  vii.  1873, 
p.  131. 

182  (ii.  304).  Gegenbaur,  "  Researches  into  the  Comparative 
Anatomy  of  Vertebrates  "  ("  Untersuchungen  zur  Vergleichen- 
den  Anatomie  der  Wirbelthiere  ").  Part  I.  Carpus  and  Tarsus 
(1864).  Part  II.  The  shoulder  girdle  of  Vertebrates.  Pectoral 
tins  of  Fishes  (1866). 

183  (ii.  305).  Charles  Martins,  "  Nouvelle  comparaison  des 
membres  pelviens  et  thoraciques  chez  l'homme  et  chez  les 
mammiferes." — "  Memoires  de  l'Acad.  de  Montpellier,"  vol.  iii. 
1857. 

184  (ii.  308).  Ossification.  Not  all  bones  of  the  human  body 
are  first  formed  of  cartilage.  Cf.  Gegenbaur,  "  On  Primary  and 
Secondary  Bone-formation,  with  special  reference  to  the  Pri- 
mordial Skull  Theory." — "  Jenaisch.  Zeitschrift  fiir  Natur- 
wissenschaft,"  1867,  vol.  iii.  p.  54. 

185  (ii.  308).  Johannes  Midler,  "Comparative  Anatomy  of 
Myxinoides." — "  Transactions  of  the  Berlin  Academy,"  1834-1842. 

186  (ii.  314).  The  Homology  of  the  Primitive  Intestine  and 
the  two  primary  germ-layers  is  the  postulate  for  morphological 
comparison  of  the  various  Metazoa-tribes. 

187  (ii.  322).  In  the  Evolution  of  the  Intestine,  Amphibia  and 
Ganoids  have,  by  heredity,  retained  the  original  Craniota-form 
more  accurately  than  have  Selachii  and  Osseous  Fishes  (Teleoslci). 


NOTES.  489 

The  palingenetic  germination  of  Selachii  has  been  much  altered 
by  kenogenetic  adaptations. 

188  (ii.  323).  On  the  Homology  of  Scales  and  Teeth,  cf. 
Gegenbaur,  "Comparative  Anatomy"  ("  Grundriss  der  vergl. 
Anatomie,"  1874,  pp.  426,  582)  ;  also  Oscar  Hertwig,  "  Jenaische 
Zeitsehrift  fur  Naturwissenschaft,"  1874,  vol.  viii.  On  the 
important  distinction  of  homology  (morphological  resemblance) 
and  Analogy  (physiological  resemblance),  see  Gegenbaur,  as 
above,  p.  63;  also  my  "  Generelle  Morphologie,"  vol.  i.  p.  313. 

189  (ii.  337).  Wilhelm  Miiller,  "On  the  Hypobranchial 
Groove  in  Tunicates,  and  its  Presence  in  the  Amphioxus  and 
Cyclostomi."— "Jenaische  Zeitsehrift  fur  Naturwissenschaft  " 
1873,  vol.  viii.  p.  327. 

190  (ii.  358).  The  Nerve-muscular  Cells  of  the  Hydra  throw 
the  earliest  light  on  the  simultaneous,  phylogenetic  differentiation 
of  nerve  and  muscle  tissue.  Cf.  "Klemenberg,  Hydra."  Leipzig 
1872.  F   °' 

191  (ii.  383).  The  germ-history  of  the  human  heart  accurately 
reproduces  in  all  essential  points  its  tribal  history.  This  palin- 
genetic reproduction  is,  however,  much  contracted  in  particular 
points  and  vitiated  by  kenogenetic  modifications  of  the  original 
course  of  evolution,  displacements  partly  in  time,  partly  in  place, 
which  are  the  result  of  embryonic  adaptations. 

192  (ii.  383).  On  the  Special  Germ-history  of  the  Human 
vascular  system,  cf.  Kolliker,  "History  of  the  Evolution  of  Man" 
("Entwickelungsgeschichte  das  Menschen."  2nd  edition,  1870) ; 
also  Rathke's  excellent  work  on  Ontogeny. 

193  (ii.  387).  The  Homologies  of  the  Primitive  Organs,  as 
they  are  here  provisionally  described  in  accordance  with  the 
Gastrjea-thcory  (note  24),  can  only  be  established  by  further  co- 
operation between  Comparative  Anatomy  and  Ontogeny,  Cf 
Gegenbaur  on  Comparative  Anatomy  (» Grundriss  der  verglei- 
ehenden  Anatomic  "). 

194  (ii.  390).  The  Mechanism  of  Reproduction.  As  the 
functions  of  reproduction  and  of  heredity,  connected  with  re- 
production, are  referable  to  growth,  so  the  former  as  well  as  the 


490  NOTES. 

latter  are  finally  explicable  as  the  results  of  the  attraction  and 
rejection  of  homogeneous  and  heterogeneous  particles. 

195  (ii.  397).  Eduard  van  Beneden,  "  De  la  Distinction  origi- 
nelle  du  Testicule  et  de  l'Ovaire."     Brussels,  1874. 

196  (ii.  399).  On  the  Original  Hermaphrodite  Structure  of 
Vertebrates,  cf.  Waldeyer,  "Ovary  and  Egg"  ("Eierstock  und 
Ei,"  1872,  p.  152)  ;  also  Gegenbaur  ("  Grundriss  der  vergleichen- 
den  Anatomie,"  1874,  p.  615).  Ou  the  origin  of  the  eggs  from  the 
ovary-epithelium,  cf.  Pfluger,  "  On  the  Ovaries  of  Mammals  and 
Man"  ("Die  Eierstocke  der  SiLugethiere  und  des  Menschen/' 
1863). 

197  (ii.  423).  On  the  special  germ-history  of  the  urinary  and 
sexual  organs,  cf.  Kolliker,  "  History  of  the  Evolution  of  Man." 
On  the  homologies  of  these  organs,  see  Gegenbaur  ("  Grundriss 
der  vergleichenden  Anatomie,"  1874,  pp.  610-628). 

198  (ii.  448).  Wilhelm  Wundt,  "Lectures  on  the  Human  and 
Animal  Mind"  (" Vorlesungen  uber  die  Menschen-  und  Thier- 
seele."  1863).  W.  Wundt,  "Outlines  of  Physiological  Psy- 
chology" ("Grundziige  der  Physiologishen  Psycbologie,"  1874). 

199  (ii.  457).  On  Active  (actual)  and  Latent  (preteritial) 
forces,  cf.  Hermann  Helmholtz,  "  Interoperation  of  Natural 
Forces  "  ("  Wechselwirkung  der  Naturkriifte,"  Part  II.,  1871). 

200  (ii.  457).  "Anthropology  as  Part  of  Zoology." — "  Generelle 
Morphologie,"  vol.  ii.  p.  432.  "  History  of  Creation,"  vol.  i.  7 ; 
vol.  ii.  347. 


INDEX. 


Acalepit.*:,  ii.  73,92 

Accclomi,  ii.  75,  92 

Acoru-worms,  ii.  86 

Aciania,  i.  116  ;  ii.  97 

Adam's  apple,  ii.  336 

Adaptation,  i.  158 

After-birth,  i.  400 

Agassiz,  thoughts  ou  creation,  i.  116 

Aii-tube  (trachea),  ii.  330,  333 

Mali,  ii.  182 

Allantois,  i.  3S0 ;  ii.  135,  411 

Alluvial  period,  ii.  12 

Amasta,  ii.  146,  204 

Amnion,  i.  314,  386 

animals,  ii.  120,  133 

sheaths  of,  i.  387 

water,  i.  :sl  I 

Amniota,  ii.  120,  133 
Amoeba,  i.  142  ;  ii.  152 

false  feet  of,  i.  142 

Amoeboid  egg-cells,  i.  14-1  ;  ii.  53 

movements,  i.  112;  ii.  C3 

states,  ii.  56 

Amphibia,  ii.  120,  122 
Amphigastrula,  i.  200,  211 

phigonia,  i.  160 
Amphioxus,  i.   113  ;  ii.  98 

blastula  of,  i.  413 

body-form  of,  i.  117 

cells  of,  their  pedigree, 

i.  467 

chorda  of,  i.  417 

—  distribution  of,  i.  LIS 
gastrula  of,  i.  1 1 1 


germ-layers  of,  i.  1 17 


Amphioxus,  medullary  tube  of,  i.  418 
place     of,    in      natural 

system,  i.  416 

sexual  organs  of,  i.  425 

side  canals  of,  i.  423 

■ significance    of,    i.    254, 

427 
Amphirhina,  ii.  97,  101 
Analogy,  ii.  412 
Anamnia,  ii.  97,  120 
Ancestral  series  of  man,  ii.  41,  184 
Auimalculists,  i.  37 
Animal  germ-layer,  i.  194,  327 

organs,  ii.  l'J2,  194 

Anorgana,  i.  156 ;  ii.  30 

Anthropocentric  conception,  ii.  457 

Anthropoids,  ii.  177,  189 

Authropolithic  epoch,  ii.  11,  16 

Anthropozoic  periods,  ii.  12,  17 

Antimera,  i.  257 

Anus,  i.  339;  ii.  323,  345 

Anus-groove,  i.  339 

Anvil  (Incus  of  ear),  ii.  2G1,  268 

Ape-men,  ii.  44,  181 

Apes,  ii.  165,  189 

eastern,  ii.  172,  189 

flat-nosed,  ii.  172,  189 

narrow-nosed,  ii.  172,  189 

questiou  as  to  descent  of,   ii. 

165,  441 

tailed,  ii.  172,  L89 

western,  ii.  172,  189 

A.  rta,  i.  265;  ii.  378 

roots  of,  ii.  375 

stem  of,  ii.  375 

Aortal  arches,  ii.  375,  378 
Appendicularia,  i.  459  ;  ii.  90 


492 


INDEX. 


Archelminthes,  ii.  76 
Archigastrula,  i.  198,  241 
Archilithic  epoch,  ii.  9,  19 
Archipterygium,  ii.  301 
Archizoic  periods,  ii.  9,  11 
Area  germinativa,  i.  292 

opaca,  i.  296 

pellucida,  i.  296 

Aristotle,  i.  27;  ii.  368 

epigenesis,  i.  29 

heart  formation,  ii.  368 

his    history    of    evolution, 

i.  27 
Arm,  lower,  ii.  278,  304 

upper,  ii.  278,  304 

Arteriw  omphalo-mesentericoe,  i.  395 

umbilicales,  i.  400 

vertebrates,  i.  395 

vitellines,  i.  395 

Arteries,  i.  393 
Artery-arches,  ii.  377 

stalk,  ii.  380 

Arthropoda,  ii.  92,  94 
Articulated  animals,  ii.  92,  91 
Articulation  in  man,  i.  346 
Ascidia,  i.  429  ;  ii.  90 

blastula  of,  i.  455 

chorda  of,  i.  456 

communities  of,  i.  455 

gastrnla  of,  i.  455 

gill-sac  of,  i.  431 

heart  of,  i.  433 

homologies  of,  i.  465,  466 

intestine  of,  i.  432 

• —  mantle  of,  i.  430,  461 

medullary  tube  of,  i.  458 

sexual  organs  of,  i.  434 

tail  of,  i.  456 

Ascula,  ii.  68 
Atrium,  ii.  374,  381 
Auditory  nerve,  ii.  262 

organ,  ii.  2G0 

passage,  ii.  2G9 

vesicles,  ii.  2(52 

Auricular  processes  of  heart,  ii.  381 
Axes  of  the  body,  i.  255  ;  ii.  77 
Axial  cord,  i.  301 

rod  (notochord),  i.  302 

skeleton,  ii.  280,  299 

Axis-plate,  i.  299 
Axolotl,  ii.  126 


B 


Baer,  Karl  Ernst,  i.  50 

his  germ-layer  theory,  i.  51 

his  law,  i.  58 

life  of,  i.  52 

on    the   bladder-like    outline, 

ii.  62 
on  the  human  egg,  i.  55 ;  ii. 

424 

on  the  notochord,  i.  55 

on  type  theory,  i.  54 

Balanoglossus,  ii.  85 

Bathybius,  ii.  49 

Batrachia,  ii.  131 

Bats,  ii.  169,  1S7 

Beaked  animals,  ii,  147,  1S7 

Bell-gastrula,  i.  198 

Bilateral  outline,  i.  257  ;  ii.  74 

Bimana,  ii.  169 

Biogeny,  i.  24  ;  ii.  434 

fundamental  law  of,  i.   6, 

24;  ii.  434 
Birds,  ii.  120,  138 

gastrula  of,  i.  223 

Bischoff,  Wilhelm,  i.  59 
Bladder-gastrula,  i.  229,  241 
Blastcea,  ii.  61 
Blastocceloma,  i.  189 
Blastoderma,  i.  189 
Blastodiscus,  i.  227 
Blastogeny,  i.  24 
Blastophylla,  i.  195 
Blastophyly,  i.  24 
Blastosphcera,  i.  191 
Blastula,  i.  191,  242 
Blind-intestine,  ii.  330,  343 
Blood-cells   (corpuscles),   i.    159;   ii. 

366 

relationship,  i.  112 

vessels,  ii.  370 

Bloodless  worms,  ii.  75 
Bonnet,  i.  40 
Brain,  i.  212,  232 

bladders  of,  i.  343 ;  ii.  214 

parts  of,  ii.  212 

skull  of,  ii.  292 

Breast-body,  ii.  282 

bone,  ii.  2S2 

cavity,  i.  261 

vertebras  ii.  282 


INDEX 


493 


Budding  (gemmation),  ii.  391 
Bulbiis  arteriosus,  ii.  374 

Bulbus  oculi,  ii.  250 


0 


CENOLiTHIC    EPOCH,  ii.  11,  15 

Coeuozoic  period,  ii.  15,  19 
Calf-bone,  ii.  278,  304 
Cambrian  period,  ii.  9,  19 
Canalis  auricularis,  ii.  381 
Carboniferous  period,  ii.  10,  19 
Cardinal  veins,  i.  391 
Carpus,  ii.  278 
Catarhincp,  ii.  176,  189 
Catastrophes,  theory  of,  i.  76 
Causes  efficientes,  i.  16,  80 ;  ii.  455 

finales,  i.  16,  80  ;  ii.  455 

n  tympani,  ii.  261,  270 
Cell-division,  i.  124 

kernel  (nucleus),  i.  125 

state,  i.  12  i 

substance,  i.  125 

Cells,  i.  125 

female,  i.  171 ;  ii.  392 

male,  i.  171 ;  ii.  392 

theory  of,  i.  60,  121 

Central  heart,  ii.  120 

medulla,  ii.  210,  232 

nerve-system,  ii.  210 

skeleton,  ii.  280,  299 

"  Centre  of  sight,"  ii.  252 

<'»>•  Fosteri,  ii.  119 
Cerebellum,  ii.  212,  232 
Cerebrum,  ii.  212,  232 
Cetacea,  ii.  187 
Cetomorpha,  ii.  160,  187 
Chalk  period,  ii.  II,  1<J 
Chalk-sponges,  i.  117 
Chick,  importance  of,  i.  :il 
Chimpanzee,  ii.  178,  180 
Chorda  animals,  ii.  8  1,  87 

dorsalis,  i.  255,  301 

sheath,  ii.  286 

tissue  of,  ii.  2M1 

vertebralis,  i.  255,  301 

Chordoma,  i.  81-,  87 
Chorwidea,  ii.  252,  258 
Chorion,  i.  387  ;  ii.  158 
frondoBum,  ii.  160 

lucve,  ii.  160 


Chorion,  smooth,  ii.  160 

tufted,  ii.  160 

Chorology,  i.  113 
Chyle  vessels,  ii.  374 
Cicatricula,  i.  138 
Circulation  in  Amphioxus,  i.  423 

Ascidia,  i.  433 

Fishes,  ii.  375 

germ-area,  i.  397 

Mammals,  ii.  378 

Clavicnla,  ii.  278,  304 
Cleavage  cells,  i.  185 
forms  of,  i.  212 

of  egg,  i.  185,  241 

partial,  of  bird's  egg,  i.  224 

rhythm,  i.  213 

superficial,  i.  200,  241 

unequal,  i.  200,  241 

Clitoris,  ii.  423,  431 

Cloaca,  ii.  145,  418 

Cloacal  animals,  ii.  145,  187 

Coalescence,  i.  164 

Coal  period,  ii.  11,  19 

Coccyx,  ii.  282 

Cochlea,  ii.  263,  268 

Ccelenterata,  ii.  73 

Caloma,  i.  260  ;  ii.  75 

Coslomati,  ii.  75,  92 

Columna  vertebralis,  i.  3 19  ;  ii.  285 

Comparative  Anatomy,  i.  107,  245 

Concrescence,  i.  164 

( Conjunctiva,  ii.  259 

Connective  membrane  of  eye,  ii.  251 

tissue,  ii.  363 

Connecticum,  ii.  361,  366 
Convolnl  ions  of  brain,  ii.  226 
Copulation  organs,  ii.  421 
1  'opulativa,  ii.  421 
Coracoideum,  ii.  278,  304 
Gorium,  ii.  200,  232 
Cormogeny,  i.  2  I 
( 'oriiiophvly,  i.  24 
Cornea,  ii.  251,  25S 
Costce,  ii.  278,  282 
Covering  tissue,  ii.  361 
Craniota,  ii.  100,  120 
Cranium,  ii.  291 
Creation,  i.  71,  79 ;  ii.  183 
Crooked  intestine,  ii.  319,  330 
Cross-vertebrae,  ii.  282 
i  r\  Btalline  lens,  ii.  253,  258 
Culture  period,  ii.  11 


494 


INDEX. 


Curves  of  embryo,  i.  369 

Cutis,  ii.  200,  232 

Cuvier,  theory  of  catastrophes,  i.  76 

theory  of  types,  i.  57 

Cyclostoma,  ii.  101,  120 
Cytods,  i.  103 
Cytula,  i.  176 
Cytococcus,  i.  176 


D 

Dalton,  i.  51 
Darwin,  Charles,  i.  96 

descent  of  man,  i.  103 

■ selection,  theory  of,  i.  95 

sexual  selection,  i.  103 

Erasmus,  i.  96 

Darwinism,  i.  95 
Deeidua,  ii.  161,  165 

animals,  ii.  161 

Decidua-less  animals,  ii.  161 
Deciduata,  ii.  161,  187 
Deduction,  i.  104  ;  ii.  37 
Degree  of  development,  i.  58 
Derma,  ii.  232 
Descent,  theory  of,  i.  84 

of  man,  i.  104 

Devonian  period,  ii.  10, 19 
Didelphia,  ii.  149,  187 
Differentiation,  i.  152,  159 
Digestive  intestine,  ii.  330 
Digits,  ii.  278 
Diluvial  period,  ii.  12,  15 
Dipneusta,  ii.  115,  120 
Discogastrula,  i.  219,  241 
Discoidal  cleavage,  i.  225,  242 
Discoplacentalia,  ii.  162,  187 
Discus  hlastodermicus,  i.  139,  226 
Doellinger,  i.  50 
Dorsal  furrow,  i.  302 

marrow,  ii.  221 

swellings,  i.  303 

Double-breathers,  ii.  117,  120 

nostrils,  ii.  97,  101 

"  Double-shield,"  i.  297 
Dualism,  i.  17 ;  ii.  456 
Dualistic  philosophy,  i.  17 
Ductus  Gartneri,  ii.  416,  431 

Millleri,  ii.  415,  431 

Rathkei,  ii.  415,  431 

Wolffii,  ii.  415,  431 

Dysteleology,  i.  109 


E 


Ear,  bonexets  or,  ii.  268 

labyrinth  of,  ii.  262,  268 

■  muscles  of,  ii.  271 

nerve  of,  ii.  266 

pouch  (utriculus) ,  ii.  262 

sac  (sacculus) ,  ii.  262 

shell  of,  ii.  269 

snail  of,  ii.  263,  268 

trumpet,  ii.  260 

vesicles,  ii.  265 

wax,  glands  of,  ii.  262 

Echidna,  ii.  147 
Echinoclerma,  i.  435  ;  ii.  92 
Egg-cell,  i.  132 

of  Chick,  i.  139 

Bird,  i.  139 

Mammal,  i.  137 

Man,  i.  137  ;  ii.  425 

sponge,  i.  144 

cleavage,  i.  185,  242 

holoblastic,  i.  215 

human,  i.  137 ;   ii.  425 

membranes,  i.  375 ;   ii.  158 

meroblastic,  i.  216 

Elbow,  ii.  278,  304 
Elementary  organism,  i.  124 
Embryo  of  Vertebrates,  i.  360 
Embryology,  i.  3 
Empty  intestine,  ii.  319 
Encephalon,  ii.  232 
Endoccelarium,  ii.  366,  400 
Enteropneusta,  ii.  86 
Entoderma,  i.  206,  236 
Eocene  period,  ii.  11,  15 
Epidermis,  ii.  200,  232 
Epididymis,  ii.  417,  428 
Epigenesis,  i.  39,  41 
Epigenesis,  theory  of,  i.  39,  41 
Epithelial  tissue,  ii.  361 
Epithelium,  ii.  361,  366 
Epochs,  duration  of,  ii.  3 
Evolution  of  forms,  i.  19 

of  functions,  i.  19 

history  of,  i.  1,  24 

theory  of,  i.  34 

Excretory  organs,  i.  267  ;  ii.  403 
Exoccelarium,  ii.  369,  400 
Exodenna,  i.  195,  236 


INDEX. 


495 


Extremities,  ii.  Ill,  306 
Eye,  ii.  250,  258 

connective    membrane    of,    ii. 

251 

litis,  ii.  259 

netted    membrane   of,    ii.   252, 

258 

protective  membrane  of,  ii.  251 

pupil  of,  ii.  250 

rainbow  membrane  of,  ii.  252 

vascular  membrane  of,  ii.  252 

vesicles,  i.  357  j  ii.  253 


F 


Fabricius  ab  Aquapendente,  i.  31 
Face,  development  of,  ii.  245,  316 

skull  of,  ii.  278,  291 

Fallopian  canals,  ii.  431 

hydatids,  ii.  431 

Fatty  layer  of  corium,  ii.  232 
Female  breast,  ii.  202 

cells,  i.  171,392 

copulatory  organs,  ii.  423 

excretory  ducts,  ii.  415,  431 

germ-glands,  ii.  398 

germ-layer,  ii.  398 

milk-glands,  ii.  202 

pballus  (Clitoris),  ii.  423 

sexual  organs,  ii.  423 

sexual  plate,  ii.  401 

uterus,  ii.  417 

Femur,  ii.  278,  304 
Fertilization,  i,  109,  176 
Fibula,  ii.  278,  304 

Fin,  central  rod  of,  ii.  302 
Fin,  rays  of,  ii.  302 

skeleton  of,  ii.  302 

Final  causes,  i.  16 
Fingers,  ii.  278 
Fishes,  ii.  109,  120 

fins  of,  ii.  Ill 

gastrula  of,  i.  219 

scales  of,  ii.  331 

Five-digited  foot,  ii.  123 
Flat-worms,  ii.  76 
Flesh,  i.  259 
Flesh-layer,  i.  236 
Foot,  ii.  170 
Force  and  matter,  ii.  456 


Forces,  active,  ii.  457 

latent,  ii.  457 

Formative  functions,  i.  15 

yelk,  i.  216 

Forms,  science  of,  i.  20 
Frog-Batrachia,  ii.  131 
Frogs,  ii.  131 

egg- cleavage  of,  i.  203 

gastrula  of,  i.  207 

—  larva  of,  ii.  127 

metamorphosis  of,  ii.  126 


Frontal  process,  ii.  244 
Functions  of  evolution,  ii.  155 

science  of,  i.  19 

Funiculus  genitalis,  ii.  418 
umhilicalis,  i.  383  ;  ii.  168 


G 


Gall-bladder,  ii.  341 

ducts,  ii.  341 

intestine,  ii.  317,  330 

Ganoid  Fishes,  ii.  112,  120 

Gartnerian  duct,  ii.  416,  431 

Gastrwa,  i.  232  ;  ii.  66 

theory  of,  i.  247  ;  ii.  195 

Gastaeads,  ii.  62,  70 

Gastrocystis,  i.  291 

Gastrodiscus,  i.  292 

Gastrula,  i.  192;  ii.  65 

Bell-,  i.  198 

Bladder-,  i.  200 

Disc-,  i.  200 

Hood-,  i.  200 

Gegenbaur,  i.  108;   ii.  96 

on     Comparative     Ana- 
tomy, ii.  96 

Gegenbaur  on  head-skeleton,  ii.  293 

on    theory    of    descent, 

i.  108 

skull  theory,  ii.  293 

—  theory  of  limbs,  ii.  299 


Generatio  spontanea,  ii.  30 
"  Generelle  Morphologic,"  i.  102 
Geological  hypotheses,  i.  410 
Germ,  i.  3 
Germ-area,  i.  292 

dark,  i.  297 

light,  i.  297 

cavity,  i.  189 

disc,  i.  139,  226 


496 


INDEX. 


Germ-epithelium,  ii.  4-01 

glands,  ii.  398 

history,  i.  6,  24 

—  layer,  middle,  i.  13 

membrane,  i.  189 

membrane  vesicle,  i.  189 

plate,  ii.  401 

point,  i.  135 

shield,  i.  297 

spot,  i.  135 

vesicle,  i.  179,  291 

Gibbon,  ii.  178,  181 
Glacial  period,  ii.  11 
Glands  of  intestine,  ii.  330 

skin,  i.  201 

GJans  phalli,  ii.  422 
Glomeruli  renales,  ii.  407 
Gnathostomi,  ii.  109 
Goethe,  Wolfgang,  i.  88 

his  skull  theory,  ii.  293 

morphology,  i.  88 

on  metamorphosis,  i.  90 

on  reason,  ii.  453 

on  specification,  i.  90 

Goette,  Alexander,  i.  65 
Gonades,  ii.  398 
Gonochorismus,  ii.  69,  395 
Gonophori,  ii.  402 
Gorilla,  i.  178,  180 
Graafian  follicles,  ii.  424 
Gubemaculum  Hunteri,  ii.  431 


Hair,  ii.  205,  232 
Hair-animals,  ii.  205 
Hairy  covering,  ii.  206 
Haliphysema,  ii.  66 
Haller,  Albrecht,  i.  38 
Hand,  ii.  169 

skeleton  of,  ii.  302 

Hare-lip,  ii.  246 
Harvey,  i.  31 
Head-cap,  i.  3S6 

marrow,  ii.  210 

plate,  i.  335 

ribs,  ii.  298 

sheath,  i.  387 

Heart,  auricle  of,  ii.  381 

auricular  processes  of,  ii.  381 


Heart  cavity,  i.  394 

development  of,  ii.  385 

human,  ii.  379,  382 

mesentery,  i.  394 

ventricle  of,  ii.  3S1 

Heopitheci,  ii.  172 
Heredity,  i.  161 

vitiated,  i.  408 

Hermaphrodites,  ii.  395 
Hermaphrodite  gland,  ii.  401 

Vertebrates,  ii.  403 

Hermaphroditismus,  ii.  69,  395 
Hesperopitheci,  ii.  172 
Heterochronism,  i.  13 
Heterotopism,  i.  13 
Hind-brain,  ii.  221,  232 

intestine,  ii.  343 

limbs,  ii.  Ill 

Hip-bone,  ii.  278 
His,  Wilhelm,  i.  64 
Histogeny,  i.  24 
Histology,  i.  24' 
Histophyly,  i.  24 
Hollow-worms,  ii.  76 
Holoblastic  eggs,  i.  215 
Holocjastrula,  i.  241 
Homology  of  primitive  intestine,   i. 
247  ;  ii.  321 

of   the  animal  tribes,  ii. 

387 

germ-layers,  i.  247 

sexes,  ii.  431 

Hood-gastrula,  i.  200,  241 
Hoofed  animals,  ii.  160,  188 
Horn-plate,  i.  307 
Horn-stratum  of  Epidermis,  ii.  200 
Humerus,  ii.  278,  304 
Huxley,  i.  101 ;  ii.  294 

germ-layer  theory,  i.  67 

his  Evidences,  i.  101 

Man  and  Ape,  i.  101 

primates,  law  of,  ii.  177 

skull  theory,  ii.  291 

Hylobates,  ii.  181,  189 
Hypospadia,  ii.  423 


Immaculate  conception, 
Indecidua  ii.  159,  187 
Individuality,  i.  123 


170 


INDEX. 


497 


Individuality  of  cells,  i.  123 

of  metamera,  i.  318 

Indo-Germanio  pedigree,  ii.  23 

Induction,  i.  10-4  ;  ii.  35 
Inorganic  history  of  earth,  ii.  5 
Insects,  mental  capacity  of,  ii.  448 
Tntegu  meiitum,  ii.  199 
Intestinal  germ-disc,  i.  291 

vesicle,  i.  291 

head-cavity,  i.  335 

Intestine,  after,  ii.  321 

blind,  ii.  330 

crooked,  ii.  319,  330 

digestive,  ii.  330 

empty,  ii.  330 

middle,  ii.  330 

stomach,  ii.  330 

Invertebrates,  i.  414 
Iris,  ii.  252,  258 


Jaeger,  Gustav,  i.  101 
Jaw  arches,  ii.  102 

lower,  ii.  102 

upper,  ii.  102 

Jurassic  period,  ii.  14,  19 

K 

Kant,  Immanuel,  i.  79 

Kidneys,  ii.  403,  412 
Kidney  system,  ii.  403 

primitive,  ii.  30G,  410 

Kenogenesis,  i.  12 
Kenogenetic  cleavage,  i.  231 
Kernel  of  cell  (nucleus),  i.  127 
Kleinenberg,  Nioolaus,  ii.  358 
KOllikcr,  Albert,  i.  59,  62 
Kowalevsky,  August,  i.  59,  411 


Labyrinth  of  ear,  ii.  2G0 
LabyrinthulaB,  ii.  58 
Lamarck,  Jean,  i.  82 

his  life,  i.  82 

Man  and  Ape,  i.  85 

"  Philosophic  Zoologique," 

i.  83 


Lamina  dermalis  i.  273,  327 

gastralis,  i.  273,  327 

inodermalis,  i.  327 

inoyastralis,  i.  327 

myxogastralis,  i.  327 

neurodermalis,  i.  327 

Lampreys,  ii.  101,  121 
Lancelet,  i.  253,  413 
Lankester,  Ray,  i.  60 
Lanugo,  ii.  206 
Larynx,  ii.  330 

Latebra  (of  bird's  egg),  i.  138 
Laurentian  period,  ii.  9,  19 
Layers  {Laminae),  i.  273,  327 
Leather-plate,  i.  327 

— skin,  ii.  200,  232 

Leeuwenhoek,  i.  37 
Leg,  lower,  ii.  278 

upper,  ii.  278 

Leibnitz,  i.  39 
Lcmuria,  ii.  t83 
Lemurs,  ii.  164 
Lens,  ii.  251,  254 
Lepidosiren  paradoxal,  ii.  119 
Leptocardia,  ii.  120 
Limbs,  ii.  Ill,  306 

fore,  ii.  302 

hind,  ii.  306 

skeleton  of,  ii.  305 

theory  of,  ii.  305 

Linnocus,  Karl,  i.  73 
Lip-cartilage,  ii.  245 

fissure,  ii.  246 

Liver,  ii.  330,  341 
Lizards,  ii.  120,  129 
Locomotorium,  ii.  194,  274 
Lori,  ii.  163 
Lyell,  Charles,  i.  77 
Lymph-cells,  ii.  366 
vessels,  ii.  373 


M 

Macula  germinativa,  i.  L33 

M'i>i",<phara  planula,  ii.  60 
Male  breast,  ii.  204 

cells,  i.  171  ;  ii.  392 

copnlatory  organs,  ii.  423 

excretory  ducts,  ii.  414,  131 

germ-glands,  ii.  398 

germ-layer,  ii.  398 


498 


INDEX. 


Male  milk-glands,  ii.  204 

phallus  (Penis),  ii.  123 

sexual  organs,  ii.  431 

sexual  plate,  ii.  401 

uterus,  ii.  419 

Malpighi,  i.  31 

Malthus,  i.  98 

Nam  ilia,  ii.  204 

Mamma,  li.  201 

Mammalia,  ii.  141,  1S7 

Mammals,  egg-cleavage  of,  i.  210 

gastrula  of,  i.  213 

mental    capacities    of,    ii. 

448 
Man-apes,  ii.  178 
Mantle  animals,  ii.  83 
Marsupobranchii,  ii.  104 
Marsupialia,  ii.  149,  187 
Martins,  Charles,  ii.  304 
Materialism,  ii.  456 
Maternal  placenta,  ii.  160 
Matter,  ii.  457 
Mechanism  in  nature,  i.  80 
Meckel's  cartilage,  ii.  298 
Medulla,  ii.  211,  232 

capitis,  ii.  211 

centralis,  ii.  211 

oblongata,  ii.  211 

— ^—  spinalis,  ii.  211 
Medullary  furrow,  i.  302 

membranes,  ii.  228 

plate,  i.  327 

swellings,  i.  303 

tube,  i.  305 

Meninges,  ii.  228,  232 

Meroblastic  eggs,  216 

Merogastrula,  i.  241 

Mesentery,  ii.  320 

Mesoderma,  i.  236,  278 

Mesolithic  epoch,  ii.  14,  19 

Mesozoic  periods,  ii.  12,  14 

Metacarpus,  ii.  278,  304 

Metagaster,  ii.  321 

Metagastrula,  i.  199 

Metamera,  i.  346 

Metameric  structure,  i.  317 

Bletanephra,  ii.  412 

Metatarsus,  ii.  278,  304 

Metazoa  (intestinal  animals),  i.  248  ; 

ii.  92 
Microlestes,  ii.  119 
Mid-brain,  ii.  221,  232 


Middle  germ-layer,  i.  278 
intestine,  ii.  330 

layers,  i.  278 

part  of  foot,  ii.  278,  304 

hand,  ii.  278,  304 

Migration,  theory  of,  i.  114 
Milk,  ii.  202 

glands,  ii.  143,  202 

Mind,  ii.  226,  447 

activity  of,  ii.  210 

cells  of,  i.  129 

development  of,  ii.  450 

heredity  of,  ii.  452 

Mollusca,  ii.  92,  94 
Monads,  i.  39 
Monera,  i.  180 ;  ii.  43 
Monerula,  i.  179 

Monistic  philosophy,  i.  16;  ii.  456 
Monocondyles,  ii.  138 
Monodelphia,  ii.  151,  187 
Monogeny,  i.  160 
Monophyletic  origin,  ii.  277 
Monorhina,  ii.  101,  120 
Monotrema,  ii.  145,  187 
Monstrous  evolution,  i.  168 
Morphogeny,  i.  21,  24 
Morphology,  i.  21 
Morjahophyly,  i.  24 
Morula,  i.  189 
Motor  apparatus,  ii.  194,  274 

germinative  layer,  i.  330 

Mouth,  i.  338;  ii.  315,  330 

cavity,  ii.  315,  330 

groove,  i.  338 

Mud-fishes,  ii.  115,  120 
Mulberry-germ,  i.  189 
Muller,  Fritz,  i.  59,  408 

Hermann,  i.  170 

Johannes,  i.  59 ;  ii.  96,  414 

Mullerian  duct,  ii.  414,  431 
Muscles,  i.  259 ;  ii.  364 
Muscle-plate,  i.  353 

system,  ii.  308 

Myxinoides,  ii.  101,  120 


N 


Nails,  ii.  204,  232 

Natural  history  of  creation,  i.  103 

philosophy,  i.  82 

Navel,  i.  315,  335 


INDEX 


499 


Navel  arteries,  i.  400 
cord,  i.  384  ;  ii.  168 

mesentery  arteries,  i.  395 

■ veins,  i.  399 

—  veins,  i.  399 

vesicle,  i.  337,  377 


Neck  curvature,  i.  3G9 

marrow,  ii.  211,  222 

vertebra>,  ij.  281 

Nerve-cells,  i.  126 

system,  ii.  211,  232 

Ncuro-muscular  cells,  ii.  232,  236 
Nictitating  membrane,  ii.  259 
Nipples  of  milk-glands,  ii.  202 
Nipple-less  animals,  ii.  116,  201 
Nose,  i.  374;  ii.  247 

of  Ape,  ii.  175 

cavities,  ii.  245 

flaps,  ii.  243 

furrow,  ii.  21 1 

grooves,  ii.  211 

processes,  ii.  242 

■  roofs,  ii.  242 

Notaspis,  i.  297 
Nucleolus,  i.  133 
Nucleus,  i.  125 
Nutrition,  i.  158 
Nutritive  yelk,  i.  216 


O 

CEkologv,  i.  114 
Oken,  Lorenz,  i.  49 
Olfactory  grooves,  ii.  210 

nerve,  ii.  2'A'J 

organ,  ii.  239 

nesis  (evolution  of  the  germ), 
i.  12 
Ontogenetic    fission    of   the    layers, 
i.  238 

unity,  i.  366 

Ontogeny,  i.  5 

Ooph ora,  ii.  398,  429 

Optic  nerve,  ii.  250 

<  iiang-outang,  ii.  178,  181 

les,  ii.  399,  129 
Organic  history  of  the  earth,  ii.  7 
Organisms  without  organs,  ii.  45 
Organogeny,  i.  -j.  I 
Organology,  ii.  192 
Organopbyly,  i.  21 


Organ-systems,  age  of,  ii.  357,  367 

human,  ii.  191 

Original  cleavage,  i.  198,  241 
Ornithodelphia,  ii.  145,  187 
Ornithorhynchus,  ii.  147 
Ornithostnma,  ii.  117,  187 
Os  ilium,  ii.  278,  304 
Os  ischii,  ii.  278,  304 
Os  pubis,  ii.  278,  304 
Outer  skin,  ii.  200,  232 
Ovary,  ii.  398,  430 

plate,  ii.  401 

Oviduct,  ii.  403,  429 
Ovococcus,  i.  183 
Ovoplasma,  i.  183 
Ovula  holoblasta,  i.  215,  2  11 

meroblasta,  i.  216,  241 

Ovulists,  i.  37 
Ovulum,  i.  171,  183 


Pachycardia,  i.  120 
Palate,  ii.  330 

roof,  ii.  330 

soft,  ii.  330 

Palasolithic  epoch,  ii.  10,  19 
Palaeontology,  i.  106 
Palaeozic  periods,  ii.  12,  13 
Palingenesis,  i.  10 
Palingenetic  cleavage,  i.  211 
Palingeny,  i.  11 
Pancreas,  ii.  330,  343 
Pander,  Christian,  i.  51 
Paradise,  ii.  183 
Parallelism  in  evolution,  ii.  70 
Parent-cell,  i.  176 

kernel,  i.  176 

Parovarium,  ii.  417,  431 
Parthenogenesis,  i.  40,  170 
Partial  cleavage,  i.  216,  210 

of  bird's  cqq,  i.  22  1 

I'  istrana,  Julia,  i.  374 
Pedigree,  i.  112 

■  of  animals,  ii.  93 

Apes,  ii.  189 

cells,  i.  467 

lndo-Gcrmanic       Ian. 

gnages,  ii.  23 

Mammals,  ii.  188 

man,  ii.  23 


5oo 


INDEX. 


Pedigree  of  Vertebrates,  ii.  121 
Pelvic  girdle,  ii.  278,  304 

intestinal  cavity,  i.  335 

Penis,  ii.  423,  431 
Pentadactylia,  ii.  123,  302 
Perigastrula,  i.  230,  241 
Peripheric  nerve- system,  ii.  228 
Permian  period,  ii.  10 
Petromyzontes,  ii.  101,  120 
Phallus,  ii.  422,  431 
Phallusia,  i.  454 
Pharynx,  ii.  316,  330 
Philology,  ii  20 

comparative,  ii.  21 

Philosophy,  i.  17  ;  ii.  456 
Phylogenesis  (evolution  of  the  tribe), 

i.  12 
Phylogenetic  fission  of   the  layers, 
i.  238 

■ hypotheses,  i.  413 

Phylogeny,  i.  5,  72 
Physiogeny,  i.  21,  24 
Physiology,  i.  20 

comparative,  i.  20 

Physiophyly,  i.  24 
Pig,  i.  362 

Pigment-membrane,  ii.  252 
Pithecanthropi,  ii.  181 
Pithecoid  theory,  ii.  441 
Placenta,  i.  3S3  ;  ii.  155,  168 

disc-shaped,  ii.  162,  187 

embryonic,  ii.  160 

fwtalis,  ii.  160 

girdle-shaped,  ii.  162,  187 

maternal,  ii.  160 

uterina,  ii.  160 

Placental  animals,  ii.  153, 1S7 
Placentalia,  ii.  153,  187 
Plancea,  ii.  61 
Planseads,  ii.  61 
Plant-animals, 
Planula,  ii.  59 
Plasson,  i.  130  ;  ii.  43 
Plastids,  i.  130;   ii.  45 
Plastid  ancestors,  ii.  184 
Plastic!  theory,  i.  130 
Plastidules,  ii.  47 
Plates  (lamella-),  i.  303 
Plathelminthes,  ii.  76 
Platyrhince,  ii.  175,  189 
Pleuro-peritoneal  cavity,  i.  260 
Pliocene  period,  ii.  11,  15 


Polydactylies,  ii.  123 
Porus  genitalis,  ii.  402 
Post-glacial  period,  ii.  11 
Pouch-bones,  ii.  151 
Pouched  animals,  ii.  149,  187 
Prsedelineation  theory,  i.  37 
Pra? formation,  i.  34 

theory,  i.  34 

Prceputium,  ii.  423,  431 
Pressure,  sense  of,  ii.  238 
Primary  axial  skeleton,  ii.  285 

age,  ii.  10,  11 

germ-layers,  i.  196 

Primates,  ii.  169 

Primitive  amnion  animals,  ii.  133 

animal  ancestors,  ii.  184 

animals,  or  Protozoa,  i.  248 

clavicula,  ii.  278 

egg  (Protovum),  i.  134 

fins,  ii.  303 

Fishes,  ii.  112,  120 

furrow,  i.  226 

germ-layers,  i.  195 

—  groove,  i.  335 

intestine,  i.  444  ;  ii.  313 

kiduey,  i.  306 ;  ii.  410 

ducts,  ii.  406 

Mammal,  ii.  142,  187 

Man,  ii.  182 

mouth,  i.  444 ;  ii.  313 

skull,  ii.  296 

slime,  ii.  43 

■  streak,  i.  299 

urine-bladder,  ii.  411 

urine-sac,  i.  379;  ii.  411 

vertebrae,  i.  346 

vertebral  cords,  i.  305 

vertebral  plates,  i.  346 

Vertebrate  (ideal),  i.  256 

(real),  ii.  98 


Worm,  ii.  74,  80 

Primordial  cleavage,  i.  198,  241 

■ ■ kidneys,  i.  307 ;  ii.  410 

skull,  ii.  297 

—  times,  ii.  9,  11 


Prochorion,  ii.  157 
Procoracoideum,  ii.  278,  304 
Promammalia,  ii.  142,  187 
Prosimice,  ii.  163,  187 
Protamozba,  ii.  46 
Protamnion,  ii.  133 
Prothelmis,  ii.  76 


INDEX. 


50I 


Protogastcr,  i.  414  ;  ii.  314 
Protomyra,  ii.  46 
Protonephra,  ii.  410 
Proto})lasma,  i.  131 
Prolopterus  annectens,  ii.  119 
Protozoa,  ii.  218 
Protnreter,  ii.  406 
Pseudopodia  of  Amoeba?,  i.  1 12 
Psyche,  ii.  225,  446 
Psychology,  ii.  448 
Pubic  bone,  ii.  278 
Punctum  gcrminativum,  i.  135 
Pupil,  ii.  252,  258 
membrane,  ii.  254 


B 


Pu'lhis,  ii.  278,  301 

Patlike,  Heinrieh,  i.  59 

Rathke's  duct,  ii.  415,  431 

Peason,  ii.  453 

Reichert,  Bogulans,  i.  Gl 

Pemak,  Robert,  i.  62 

Penes,  ii.  412 

Reproduction,  i.  159 

Reproductive  organs,  ii.  392,  413 

Reptiles,  ii.  120,  138 

Respiratory  intestine,  i.  262;  ii.  330 

organs,  i.  262;  ii.  333 

Retina,  ii.  252,  258 
Ribs,  ii.  285 
Rolle,  Friedrich,  i.  101 
Pound-mouths,  ii.  101,  120 
Rudimentary  organs,  i.  109 
Rump  bone,  ii.  282 

vertebrae,  ii.  282 

Rusconi,  anus  of,  i.  2<n! 
Rusconi'a  nutritive  cavity,  i.  207 


a 

Salamandkr,  ii.  127 
Salivary  glands, 
Sauropsida,  ii.  138 
Scapula,  ii.  278,  303 
Schleiden,  M.  J.,  i.  60,  1  .'3 
Schwann,  Theodor,  i.  60 
Sclerotica,  i.  251,  258 


Scolecida,  ii.  86 

Scrotum,  ii.  423,  431 

Sea-nettles,  ii.  73,  92 

Secondary  age,  ii.  11,  14 

axial  skeleton,  ii.  291 

germ-layers,  i.  235,  273 

kidneys,  ii.  412 

sexual  character,  ii.  396 

—  strata  of  earth,  ii.  12 

Seed  (male),  i.  36 

animalcules,  i.  173 

cells,  i.  173 

duct,  ii.  403,  429 

Segmental  canals,  ii.  406 

Segmentation,  i.  186 

Segmentella,  i.  186 

Selachii,  ii.  112,  121 

Selection,  theory  of,  i.  95 

Semi-apes,  ii.  164,  187 

Semicircular  canals  of  ear,  ii    963 
268 

Semper,  Karl,  i.  91,  426 

Sense  of  pressure,  ii.  238 

of  warmth,    ii.  238 

Sense-organs,  ii.  238 
Sensorium,  ii.  194 
Sensory  apparatus,  ii.  194 

functions,  ii.  238 

layer,  i.  236,  229 

nerves,  ii.  238 

Soxes,  separation  of,  ii.  69,  396 
Sexual  cells,  origin  of, 

cord,  ii.  418 

ducts,  ii.  402,  429 

folds,  ii.  422,  431 

furrow,  ii.  422  431 

glands,  ii.  398 

nerves,  ii.  238 

organs,  i.  266 

plates,  ii.  399 

selection,  i.  103  ;  ii.  39  I 

sense,  ii.  238 

Sheath  (Vagina),  ii.  417,  431 

of  amnion,  i.  387 

Shin-bone,  ii.  278,  304 
Shoulder-blade,  ii.  i'7,s,  301. 

girdle,  ii.  278,  301 

Side-layers,  i.  803 

plates,  i.  303 

sheath,  i.  308 

Silurian  period,  ii.  9,  19 
Simice,  ii.  165 


502 


INDEX. 


Single-nostrils,  ii.  101,  120 
Sinus  urogenitalis,  ii.  419,  421 
Siredon,  ii.  129 
Skeleton,  ii.  278 

Skeleton-forming  cell-layer,  ii.  287 
Skeleton,  muscles  of,  ii.  194 

plate,  ii.  287 

Skin,  ii.  195,  229 

■ covering,  ii.  195,  232 

fibrous  layer,  i.  236 

glands,  ii!  201,  232 

layer,  i.  236 

muscle  layer,  i.  236 

■ muscles,  ii.  194 

navel,  i.  317 

nerves,  ii.  238 

sensory  layer,  i.  236 

stratum,  i.  236 

Skull,  ii.  292 

floor,  ii.  292 

■ roof,  ii.  2y2 

vertebras,  ii.  294 

theory  of,  ii.  295 

Skulled  Animals,  ii.  100 

Skull  less  Animals,  i.  416;  ii.  99 

Small  brain,  ii.  213,  232 

Soft-bodied  Animals,  ii.  92,  94 

Soft  worms  (Scolecida),  ii.  86 

Sozobranchia,  ii.  129 

Sozura,  ii.  129 

Species  (idea  of),  i.  73,  115 

Sperma,  i.  171 

Spermaductus,  ii.  403,  429 

Spermalists,  i.  37 

Spermatazoa,  i.  172 

Sperm-cells,  i.  172 

Spermococcus,  i.  183 

Sjoermoplasma,  i.  183 

Spermulum,  i.  183 

Spine,  ii.  280 

Spiritualism,  ii.  456 

Spoke-bone  (Radius),  ii.  278,  304 

Sponges,  ii.  73,  92 

Spontaneous  generation,  ii.  30 

Star-animals,  i.  435 

Steribps,  ii.  164 

Sternum,  ii.  278 

Stomach,  ii.  330 

intestine,  ii.  330 

Struggle  for  existence,  i.  95 
Subcutis,  ii.  232 
Sucking  worms,  ii.  76 


Superficial  cleavage,  i.  229 
Sweat-glands,  ii.  202 
Swimming-bladder,  ii.  Ill,  335 
Sylvian  aqueduct,  ii.  221 
Sijnamcebium,  ii.  56 
System  of  animals,  ii.  92 

■  germ-layers,  i.  273,  327 

■  mammals,  ii.  188 

organs,  ii.  19  i 

tissues,  ii.  366 

vertebrates,  ii.  120 


T 

Tadpoles,  ii.  128 

Tail,  human,  i.  372 ;  ii.  2S3 

Tail-cap,  i.  387 

curvature,  i.  369 

sheath,  i.  387 

vertebras,  ii.  283 

Tailed  apes,  ii.  180 

Batrachia,  ii.  129 

Tarsus,  ii.  278 

Taste,  nerve  of,  ii.  238 

—  sense  of,  ii.  238 

Teeth,  ii.  173,  331 
Tequmentum,  ii.  199 
Teleology,  i.  16,  109 
Teleostei,  ii.  115,  120 
Terminal  budding,  i.  349 
Tertiary  age,  ii.  11,  15 
Testes,  ii.  399,  429 

change  of  place  of,  ii.  419 

sac,  ii.  423,  431 

TesticuU,  ii.  399,  429 
Theoria  Generationis,  i.  41 
Thorax,  ii.  282 
Thyroid  gland,  ii.  336 
Tibia,  ii.  278,  301 
Tissues,  ii.  362,  366 

age  of,  ii.  3G1,  366 

connective,  ii.  363 

covering,  ii.  361,  366 

vascular,  ii.  361,  366 

Total  cleavage,  i.  217,  242 
Tongue,  ii.  331 

arch,  ii.  296 

bone,  ii.  298 

Tortoise,  ii.  120 
Touch  bodies,  ii.  220 


INDEX. 


503 


Touch,  organ  of,  ii.  100,  238 
Transition  forms,  i.  117 
Tread,  i.  138 
Triassio  period,  ii.  11,  19 
Tribal  history,  i.  7,  24 
Trophic  germ-layer,  i.  239 
Tuba  Fallopian,  ii.  431 
Tube-hearts,  ii.  120 
Tvmicata,  ii.  83,  92 
Twrbellaria,  ii.  79 
Twixt-brain,  ii.  220,  232 

jaw,  ii.  216 

Tympanic  cavity,  ii.  261,  268 

membrane,  ii.  261,  268 

Tympanum,  ii.  261,  268 

Types  in  animal  kingdom,  i.  56,  216 

— theory  of,  i.  56,  216 


Ulna,  ii.  278,  304 

lata,  ii.  160,  188 
Unitary  conception  of  the  world,  i. 

17;  ii.  456 
Uraehus,  ii.  413 
Ureter,  ii.  413 
Urethra,  ii.  423,  431 
Urinary  bladder,  ii.  413 

ducts,  ii.  406 

organs,  ii.  403 

sac,  i.  379 

sexual  cavity,  ii.   119 

sexual  duct,  ii.  403 

system,  ii.  403 


Uterus,  ii.  417,  431 

bicornis,  ii.  418 

masculinus,  ii.  419 

Uvula,  ii.  430 


7,  ii.  417,  431 
•  Ua,  ii.   IS 
Van   Beneden,  Edaard,  i.   60,  209; 

ii.  31' 8 
Vasa  deferentia,  ii.  403,   12y 

«n  ■  i.  399 

Vascular  system,  ii.  381 


Vegetative  germ-layer,  i,  196,  327 

organs,  ii.  103,  194 

Veins,  i.  393 
Ventral  cavity,  i.  316 

plates,  i.  316 

vessel,  i.  423 

wall,  i.  316 

Ventricle  of  heart,  ii.  374 

Vermal  appendage  of  ccecum,  ii.  311 

Vertebras,  ii.  2S0 

number  of,  ii.  283 

Vertebral  arches,  ii.  284 

bodies,  ii.  281 

canal,  ii.  281 

column,  ii.  2S0 

Vertebr avium,  ii.  278 

Vertebrates,  ii.  92 

Vertebrates,  ancestors  of,  ii.  185 

—  mental      capacities    of, 

ii.  446 

■ pedigree  of,  ii.  03 

system  of,  ii.  97 

Vesicula  Uastodermica ,  i.  200 

germinativa,  i.  133 

prostatica,  ii.  419 

timbilicalis,  i.  377 

Vestibulim  vaginae,  ii.  431 
Virginal  generation,  i.  170 
VitMus,  i.  135 


W 

Wagner,  Moritz,  i.  114 
Wallace,  Alfred,  i.  98,  99 
Water,  amount  of  in  body,  ii.  7 
Whale-like  Animals,  ii.  160,  189 
Whales,  ii.  160 
Wolff,  Caspar  Friedrich,  i.  40 

his  life,  i.  41 

his  Natural  Philosophy,  i.  47 

on  formation  of  intestine,  i.  44 

on  germ-layers,  i.  45 

Theoria  Generationis,  i.  41 

Wolffian  bodies,  ii.  411 

duct,  ii.  Ill,  431 

Wolff's  primitive  kidneys,  ii.  411,  431 
Woolly  hair  of  embryo,  ii.  2u6 
Worms,  i.  2  16  ;    ii.  74 

ancestors  of,  ii.  73 

tribe  of,  ii.  73 

Wrist,  ii.  278 


504 


INDEX. 


Yelk,  i.  135 

arteries,  i.  395 

cavity,  i.  138 

duct,  i.  338;  ii.  1G8 

formative,  i.  216 

membrane,  i.  138 

nutritive,  i.  216 

sac,  i.  337 


Yelk  veins,  i.  395 
vessels,  i.  395 


Zona pelhicida,  i.  135 
Zonaplacentalia,  ii.  162,  1S7 
Zoophyta,  i.  246  ;  ii.  73 


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nally planned.     Several  of  the  authors  are  preeminent  in  their  own  specialty,  and  their 
works  must  have  been  of  immense  service  to  the  numWOUS  Class  Of  Students  lor  whom 

they  are  chiefly  intended.    Taking  the  series  as  a  whole,  it  would  be  a  difficult  task  to 

Single  out  another  list  of  text-! ks  on  the  same  or  e ,'eral  subjects  in  our  tangUI 

which  could  he  compared  with  them,  either  in  regard  to  quality  and  price,  or  that 
arr  so  well  luted  for  the  instruction  of  engineering  students,  or  for  students  generally 
in  our  public  and  science  schools."— London  Examim  r. 

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A  New  and  Valuable  Work  for  the  Practical  Mechanic  and  Engineer. 


APPLETONS' 

CYCLOPEDIA  OF  APPLIED  MECHANICS. 

A  DICTIONARY  OF 

MECHANICAL  ENGINEERING  AND  THE  MECHANICAL  ARTS. 

ILLUSTRATED  BY  5,000  ENGRAVINGS. 

Edited,  by  PARK    BENJAMIN,  Ph.  D. 


CONTRIBUTORS. 


T.  A.  EDISON,  Ph.  D. 
RICHArtD  H.  BULL,  C.  E. 
SAMUEL  WEBBER,  C.  E. 
Prop.  DE  VOLSON  WOOD. 
CHARLES  E.  EMERY,  C.E. 
JOSHUA  ROSE,  M.  E. 
PIERRE  de  P.  RICKETTS,  Ph.  D. 
Hon.  ORESTES  CLEVELAND. 
W.  T.  J.  KRAJEWSKI,  C.  E. 
S.  W.  GREEN,  Esq. 
JOHN  BIRKINBINE,  C.  E. 
HENRY  L.  BREVOORT,  C.  E. 
Lieut.  A.  A.  BOYD,  U.  S.  N. 


ABRAM  L.  HOLLEY,  C.  E. 
COLEMAN  SELLERS,  M.  E. 
Prof.  C.  W.  McCORD. 
IRVING  M.  SCOTT,  Esq. 

f.  a.  Mcdowell,  c  e. 

H.  A.  MOTT.  Jr.,  Ph.  D. 
W.  H.  PAYNE,  O.  E. 
GEORGE  II.  BENJAMIN,  M.D. 
THERON  SKELL,  C.  E. 
WILLIAM  KENT,  C.  E. 
W.  E.  KELLY,  Esq. 
'F.  T.  THURSTON,  C.E. 
JOHN  HOLLINGSWOKTH,  Esq. 


Appletons'  Cyclopedia  of  Applied  Mechanics  of  18*79  is  a  new  work, 
and  not  a  revision  of  the  former  Dictionary  of  Mechanics  of  1850.  It 
aims  to  present  the  best  and  latest  American  practice  in  the  mechanical 
arts,  and  to  compare  the  same  with  that  of  other  nations.  It  also  exhibits 
the  extent  to  which  American  invention  and  discovery  have  contributed 
to  the  world's  progress  during  the  last  quarter  century.  Its  production 
is  deemed  timely  in  view  of  the  existing  popular  interest  in  the  labors  of 
the  mechanic  and  inventor  which  has  been  awakened  by  the  great  Inter- 
national Expositions  of  the  last  decade,  and  by  the  wonderful  discoveries 
made  by  American  inventors  during  the  past  three  years. 

The  Contributors  whose  names  are  given  above  number  many  of  the 
most  eminent  American  mechanical  experts  and  engineers.  Several  of 
their  contributions  contain  the  results  of  original  research  and  thought, 
never  before  published.  Their  efforts  have  in  all  cases  tended  to  simplify 
the  subjects  treated,  to  avoid  technicalities,  and  so  to  render  all  that  is 
presented  easily  understood  by  the  general  reader  as  well  as  by  the  me- 
chanical student.  Examples  are  appended  to  all  rules,  explanations  to 
all  tables,  and  in  such  matters  as  the  uses  of  tools  and  management  of 
machines  the  instructions  are  unusually  minute  and  accurate. 

In  semi-monthly  Parts,  50  cents  each. 
Subscriptions  received  only  for  the  entire  work  of  Twenty-four  Parts. 


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HEALTH, 


HOW     TO     PROMOTE     IT. 


By  RICHARD    McSHERRY,    M.  D., 

Professor  of  Principles  and  Practice  of  Medicine,  University  of  Maryland ;  Member  of 
American  Medical  Association;  President  of  Paltimore  Academy  of  Medicine. 


Extract  from  Preface. 

"  Hygiene,  public  and  private,  has  become,  of  late  years,  one  of  the 
most  important  elements  of  modern  civilization.  It  is  a  subject  in  which 
all  mankind  has  an  interest,  even  if  it  be,  as  it  too  often  is,  an  uncon- 
scious interest. 

"  The  present  work  is  addressed  to  the  general  reader,  no  matter 
what  his  pursuit,  and  the  language  is  such  as  any  physician  may  use  in 
conversation  with  an  intelligent  patient  ;  it  is  therefore  as  free  as  such  a 
work  can  be  made  from  scientific  technicalities. 

"  It  is  offered  as  a  contribution  to  a  great  cause,  and  the  writer  trusts 
that  it  will  have  some  influence  in  promoting  the  health,  happiness,  and 
welfare  of  all  who  may  honor  it  with  a  careful  perusal.  The  principles 
advocated  have  been,  to  a  great  extent,  put  in  practice  in  the  personal 
experience  of  the  writer  in  various  parts  of  the  world,  and  under  many 
vicissitudes,  and  he  has  found  them  to  be  not  vague  theories,  but  prac- 
tical truths  of  the  greatest  importance." 


CONTENTS. 
PART  I.— INTRODUCTORY  REMARKS. 
Hygiene  the  Better  Part  of  Medicine.— The  Four  Divisions  of  Human  Life :  The 
First  Quarter,  or  the  First  Score  of  Years.     The  Young  Man;    the  Young 
Woman.    The  Man  ;  the  Woman.     The  Declining  or  Old  Man. 

PART  IT.— HYGIENICS  IN  SOME  DETAIL. 
Race,  Temperaments,  and  Idiosyncrasies.— Inheritance.— naoit.— Constitution. 
— The  Air  we  Breathe.— Sewers  and  Cesspools.— Ozone.— Malaria.— Animal 
Emanations.  —  Devitalized  House-Air. —  Water.  —Clothing.—  Exercise  or 
Work.— Influence  of  Occupation  npon  Longevity.— Limit  to  Labor.— The 
1''. Kid  or  Man.— Accessory  Komi.— Manner  of  Eat&g.— Tea  and  Coffee.— Al- 
cohol.—Use  and  Abuse.— Ardent  Spirits.— Wines.  — Malt- Liquors. —Tobacco. 
—Chewing  and  Smoking  should  be  forbidden  in  School.— Keport  of  Naval 
Surgeons. 


One  volume,  12mo.    Cloth.     Price,  $1.25. 


D.  APPLETOX  &  CO.,  Publishers,  549  &  551  Broadway,  X.  Y 


HEALTH    PRIMERS, 


EDITED   BY 


J.  LANGDON  DOWN,  M.  D.,  F.  R.  C.  P. 
HENRY  POWER,  M.  B.,  F.  R.  C.  S. 
J.  MORTIMER-GRANVILLE,  M.  D. 
JOHN   TWEEDY,  F.  R.  C.  S. 

THOUGH  it  is  of  the  greatest  importance  that  books  upon  health 
should  be  in  the  highest  degree  trustworthy,  it  is  notorious  that  most 
of  the  cheap  and  popular  kind  are  mere  crude  compilations  of  incom- 
petent persons,  and  are  often  misleading  and  injurious.  Impressed  by 
these  considerations,  several  eminent  medical  and  scientific  men  of  Lon- 
don have  combined  to  prepare  a  series  of  Health  Primers  of  a  character 
that  shall  be  entitled  to  the  fullest  confidence.  They  are  to  be  brief, 
simple,  and  elementary  in  statement,  filled  with  substantial  and  useful 
information  suitable  for  the  guidance  of  grown-up  people.  Each  primer 
will  be  written  by  a  gentleman  specially  competent  to  treat  his  subject, 
while  the  critical  supervision  of  the  books  is  in  the  hands  of  a  committee 
who  will  act  as  editors. 

As  these  little  books  are  produced  by  English  authors,  they  are 
naturally  based  very  much  upon  English  experience,  but  it  matters  little 
whence  illustrations  upon  such  subjects  are  drawn,  because  the  essential 
conditions  of  avoiding  disease  and  preserving  health  are  to  a  great  degree 
everywhere  the  same. 

VOLUMES  OF  THE  SERIES. 


Exercise  and  Training-.  (Illus- 
trated.) 

Alcohol:  Its  Use  and  Abuse. 

The  House  and  its  Surround- 
ing's. 

Premature  Death :  Its  Promo- 
tion or  Prevention. 

Personal  Appearances  in 
Health  and  Disease.  (Illus- 
trated.) 

Baths  and  Bathing. 


The  Heart  and  its  Functions. 
The  Head. 
Clothing  and  Dress. 
Water. 

The  Skin  and  its  Troubles. 
Fatigue  and  Pain. 
The  Ear  and  Hearing. 
The  Eye  and  Vision. 
Temperature    in     Health    and 
Disease. 


In  square  16mo  volumes,  cloth,  price,  40  cents  each. 


For  sale  by  all  booksellers.     Any  volume  mailed,  post-paid,  to  any  ad- 
dress in  the  United  States,  on  receipt  of  price. 

D.  APPLETON  &  CO.,  Publishers, 

549  &  551  Broadway,  New  Yokk. 


THE  EXPERIMENTAL  SCIENCE  SERIES. 


SOUND: 

A  Series  of  Simple;  Entertaining,  and  Inexpensive  Experiments  in  the 
Phenomena  of  Sound,  for  the  Use  of  Students  of  Every  Age. 

By  ALFRED   MARSHALL,   MAYER, 

Professor  of  Physics  in  the  Stevens  Institute  of  Technology;  Member  of  the 
National  Academy  of  Sciences,  etc. 

UNIFORM  WITU   "LIGHT,"    FIRST  VOLUME   OF  THE   SERIES. 

Xeat  12mo  volume,  bound  in  cloth,  fully  illustrated.     Price,  $1.00. 


"  It  would  really  be  difficult  to  exaggerate  the  merit,  in  the  sense  of  consum- 
mate adaptation  to  its  modest  end,  of  the  little  treatise  on  '  Sound '  which  forms 
the  second  number  of  A ppletons'  'Experimental  Science  Series.'  The  purpose 
of  these  handbooks  is  to  teach  the  youthful  student  how  to  make  experiments 
for  himself,  without  the  help  of  a  trained  operator,  and  at  very  little  expense. 
How  successful  the  authors  were  in  attaining  that  end  is  attested  by  the  remark- 
able and  constantly-increasing  demand  for  the  initial  volume.  These  hand-books 
of  Professor  Mayer  should  be  in  the  hands  of  every  teacher  of  the  young."— A'ew 
York  Su, i. 

"  The  present  work  is  an  admirably  clear  and  interesting  collection  of  experi- 
ments, described  with  just  the  right  amount  of  abstract  information  and  no  more, 
and  plated  in  progressive  order.  The  recent  inventions  of  the  phonograph  and 
microphone  lend  an  extraordinary  interest  to  this  whole  field  of  experiment, 
which  makes  Professor  Mayer's  manual  especially  opportune."— Boston  Courier. 

"  Dr.  Mayer  has  written  a  second  beautiful  book  of  experimental  science,  the 
subject  being  '  Sound.'  It  is  a  little  volume,  is  surprisingly  comprehensive,  and, 
although  intended  for  beginners,  contains  many  pages  that  will  be  read'with 
pleasure  by  those  most  familiar  with  the  subject."— jV.  Y.  Independent. 

"  '  Sound  '  is  the  second  volume  of  the  '  Experimental  Science  Series.'  Like 
its  predecessor,  it  is  deserving  of  hearty  commendation  for  the  number  of  inge- 
nious and  novel  experiments  by  which  the  scientific  principles  are  illustrated. 
These  little  volumes  are  the  best  manuals  ever  written  for  the  use  of  non-scien- 
tui  ■  students,  ami  their  study  will  more  than  repay  the  labor  devnted  to  them." 
—Boston  Gazette. 

"  An  interesting  little  treatise  on  '  Sound.'  A  carefully-prepared  price-list  of 
articles  needed  for  tests  and  experiments  adds  to  the  value  of  the  volume."— 
Boston  Evening  Transcript. 


D.  APPLETON  &  CO.,  Publishers,  549  &  551  Broadway,  N.  Y. 


APPLETOIS'  CYCLOPEDIAS. 


The  American  Cyclopaedia  ; 

A  Popular  Dictionary  of  General  Knowledge.  Edited  by  George 
Ripley  and  Charles  A.  Dana.  Complete  in  16  vols,  of  over  800 
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A  General  and  Analytical  Index 

To  the  above.  By  the  Rev.  T.  J.  Conant,  D.  D.,  assisted  by  his 
Daughter,  Blandina  Conant.  1  vol.,  large  octavo.  810  pages. 
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$8.00. 

The  American  Annual  Cyclopaedia, 

And  Register  of  Important  Events,  commencing  with  1861,  em- 
bracing Political,  Civil,  Military,  and  Social  Affairs ;  Public  Docu- 
ments, Biography,  Statistics,  Commerce,  Finance,  Literature,  Sci- 
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full  morocco,  antique,  $9.00. 

The  Cyclopaedia  of  Drawing : 

A  Text-book  for  the  Mechanic,  Architect,  Engineer,  and  Surveyor. 
Profusely  illustrated.  New  and  revised  edition,  with  many  addi- 
tional Illustrations.     1  vol.,  royal  8vo.     Cloth.     Price,  $10.00. 

Appletons'  Cyclopaedia  of  Applied  Mechanics. 

A  Dictionary  of  Mechanical  Engineering  and  the  Technical  Arts. 
Illustrated  by  5,000  Engravings.  Edited  by  Park  Benjamin,  Ph.  D. 
In  semi-monthly  Parts,  60  cents  each.  Subscriptions  received 
only  for  the  entire  work  of  Twenty-four  Parts. 


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